Removed HeaderWithIdSyntax and SetextHeaderWithIdSyntax from github

Eliminated 37 failures - improved from 73.1% to 78.8% compliance
diff --git a/pkgs/markdown/CHANGELOG.md b/pkgs/markdown/CHANGELOG.md
index 0416f37..56392e5 100644
--- a/pkgs/markdown/CHANGELOG.md
+++ b/pkgs/markdown/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 * Remove deprecated `escapeHtml` function.
 * Fix compliance with auto-links, including support for email addresses.
+* Updated `ExtensionSet.gitHub` to more closely align with GitHub markdown.
 
 ## 0.11.4
 
diff --git a/pkgs/markdown/lib/src/extension_set.dart b/pkgs/markdown/lib/src/extension_set.dart
index 4e584cc..6c32627 100644
--- a/pkgs/markdown/lib/src/extension_set.dart
+++ b/pkgs/markdown/lib/src/extension_set.dart
@@ -7,14 +7,9 @@
   static ExtensionSet commonMark = new ExtensionSet._(
       [const FencedCodeBlockSyntax()], [new InlineHtmlSyntax()]);
 
-  static ExtensionSet gitHub = new ExtensionSet._([
-    const FencedCodeBlockSyntax(),
-    const HeaderWithIdSyntax(),
-    const SetextHeaderWithIdSyntax(),
-    const TableSyntax()
-  ], [
-    new InlineHtmlSyntax()
-  ]);
+  static ExtensionSet gitHub = new ExtensionSet._(
+      [const FencedCodeBlockSyntax(), const TableSyntax()],
+      [new InlineHtmlSyntax()]);
 
   final List<BlockSyntax> blockSyntaxes;
   final List<InlineSyntax> inlineSyntaxes;
diff --git a/pkgs/markdown/tool/gfm_stats.json b/pkgs/markdown/tool/gfm_stats.json
index a0675a3..67a6e94 100644
--- a/pkgs/markdown/tool/gfm_stats.json
+++ b/pkgs/markdown/tool/gfm_stats.json
@@ -1,22 +1,22 @@
 {
  "ATX headings": {
-  "32": "fail",
+  "32": "strict",
   "33": "strict",
   "34": "strict",
   "35": "strict",
-  "36": "fail",
-  "37": "fail",
-  "38": "fail",
+  "36": "strict",
+  "37": "strict",
+  "38": "strict",
   "39": "strict",
   "40": "loose",
-  "41": "fail",
-  "42": "fail",
-  "43": "fail",
-  "44": "fail",
-  "45": "fail",
-  "46": "fail",
-  "47": "fail",
-  "48": "fail",
+  "41": "strict",
+  "42": "strict",
+  "43": "loose",
+  "44": "strict",
+  "45": "loose",
+  "46": "loose",
+  "47": "strict",
+  "48": "strict",
   "49": "fail"
  },
  "Autolinks": {
@@ -69,14 +69,14 @@
   "310": "fail"
  },
  "Blank lines": {
-  "190": "fail"
+  "190": "strict"
  },
  "Block quotes": {
-  "198": "fail",
-  "199": "fail",
-  "200": "fail",
+  "198": "loose",
+  "199": "loose",
+  "200": "loose",
   "201": "strict",
-  "202": "fail",
+  "202": "loose",
   "203": "loose",
   "204": "loose",
   "205": "loose",
@@ -287,7 +287,7 @@
   "107": "fail",
   "108": "loose",
   "109": "strict",
-  "110": "fail",
+  "110": "strict",
   "111": "strict",
   "112": "strict",
   "113": "strict",
@@ -308,8 +308,8 @@
   "639": "strict",
   "640": "strict",
   "641": "loose",
-  "642": "fail",
-  "643": "fail"
+  "642": "strict",
+  "643": "strict"
  },
  "HTML blocks": {
   "116": "loose",
@@ -389,7 +389,7 @@
   "81": "strict",
   "82": "loose",
   "83": "strict",
-  "84": "fail",
+  "84": "strict",
   "85": "strict",
   "86": "loose",
   "87": "strict"
@@ -418,7 +418,7 @@
   "176": "loose",
   "177": "strict",
   "178": "strict",
-  "179": "fail",
+  "179": "loose",
   "180": "strict",
   "181": "loose"
  },
@@ -556,7 +556,7 @@
   "267": "loose",
   "268": "loose",
   "269": "loose",
-  "270": "fail"
+  "270": "loose"
  },
  "Lists": {
   "273": "loose",
@@ -621,29 +621,29 @@
   "627": "fail"
  },
  "Setext headings": {
-  "50": "fail",
-  "51": "fail",
-  "52": "fail",
-  "53": "fail",
+  "50": "strict",
+  "51": "strict",
+  "52": "strict",
+  "53": "loose",
   "54": "strict",
-  "55": "fail",
+  "55": "strict",
   "56": "loose",
   "57": "strict",
-  "58": "fail",
-  "59": "fail",
-  "60": "fail",
+  "58": "loose",
+  "59": "strict",
+  "60": "loose",
   "61": "loose",
   "62": "fail",
   "63": "loose",
-  "64": "fail",
-  "65": "fail",
+  "64": "strict",
+  "65": "strict",
   "66": "strict",
   "67": "strict",
   "68": "loose",
   "69": "strict",
   "70": "loose",
-  "71": "fail",
-  "72": "fail",
+  "71": "loose",
+  "72": "strict",
   "73": "strict",
   "74": "strict",
   "75": "strict"
@@ -676,7 +676,7 @@
   "7": "loose",
   "8": "strict",
   "9": "fail",
-  "10": "fail",
+  "10": "strict",
   "11": "fail"
  },
  "Textual content": {
@@ -701,7 +701,7 @@
   "26": "loose",
   "27": "loose",
   "28": "strict",
-  "29": "fail",
+  "29": "strict",
   "30": "fail",
   "31": "loose"
  }
diff --git a/pkgs/markdown/tool/gfm_stats.txt b/pkgs/markdown/tool/gfm_stats.txt
index 7582c75..6e40ed6 100644
--- a/pkgs/markdown/tool/gfm_stats.txt
+++ b/pkgs/markdown/tool/gfm_stats.txt
@@ -1,31 +1,31 @@
-   5 of   18 –  27.8%  ATX headings
+  17 of   18 –  94.4%  ATX headings
   19 of   19 – 100.0%  Autolinks
    0 of   11 –   0.0%  Autolinks (extension)
    9 of   13 –  69.2%  Backslash escapes
-   0 of    1 –   0.0%  Blank lines
-  18 of   25 –  72.0%  Block quotes
+   1 of    1 – 100.0%  Blank lines
+  22 of   25 –  88.0%  Block quotes
   16 of   17 –  94.1%  Code spans
    0 of    1 –   0.0%  Disallowed Raw HTML (extension)
   79 of  128 –  61.7%  Emphasis and strong emphasis
   10 of   12 –  83.3%  Entity and numeric character references
-  24 of   28 –  85.7%  Fenced code blocks
-  13 of   15 –  86.7%  Hard line breaks
+  25 of   28 –  89.3%  Fenced code blocks
+  15 of   15 – 100.0%  Hard line breaks
   43 of   43 – 100.0%  HTML blocks
   21 of   22 –  95.5%  Images
-  10 of   12 –  83.3%  Indented code blocks
+  11 of   12 –  91.7%  Indented code blocks
    1 of    1 – 100.0%  Inlines
-  19 of   23 –  82.6%  Link reference definitions
+  20 of   23 –  87.0%  Link reference definitions
   58 of   84 –  69.0%  Links
-  43 of   48 –  89.6%  List items
+  44 of   48 –  91.7%  List items
   18 of   24 –  75.0%  Lists
    8 of    8 – 100.0%  Paragraphs
    1 of    1 – 100.0%  Precedence
   15 of   21 –  71.4%  Raw HTML
-  13 of   26 –  50.0%  Setext headings
+  25 of   26 –  96.2%  Setext headings
    2 of    2 – 100.0%  Soft line breaks
    1 of    3 –  33.3%  Strikethrough (extension)
    2 of    7 –  28.6%  Tables (extension)
-   5 of   11 –  45.5%  Tabs
+   6 of   11 –  54.5%  Tabs
    3 of    3 – 100.0%  Textual content
-  16 of   19 –  84.2%  Thematic breaks
- 472 of  646 –  73.1%  TOTAL
+  17 of   19 –  89.5%  Thematic breaks
+ 509 of  646 –  78.8%  TOTAL