Fixes dart-lang/markdowndart-lang/markdown#86. Linebreaks should not be treated as `TextSyntax` but should be a subclass of `InlineSyntax`. This also requires a small modification to HtmlRenderer to put a \n after each <br />; this makes all the unit tests pass.

diff --git a/pkgs/markdown/lib/src/html_renderer.dart b/pkgs/markdown/lib/src/html_renderer.dart
index 184f9f9..03977ca 100644
--- a/pkgs/markdown/lib/src/html_renderer.dart
+++ b/pkgs/markdown/lib/src/html_renderer.dart

@@ -85,6 +85,11 @@
     if (element.isEmpty) {
       // Empty element like <hr/>.
       buffer.write(' />');
+
+      if (element.tag == 'br') {
+        buffer.write('\n');
+      }
+
       return false;
     } else {
       buffer.write('>');

diff --git a/pkgs/markdown/lib/src/inline_parser.dart b/pkgs/markdown/lib/src/inline_parser.dart
index a008ca8..52ee24e 100644
--- a/pkgs/markdown/lib/src/inline_parser.dart
+++ b/pkgs/markdown/lib/src/inline_parser.dart

@@ -14,6 +14,7 @@
   static final List<InlineSyntax> _defaultSyntaxes =
       new List<InlineSyntax>.unmodifiable(<InlineSyntax>[
     new AutolinkSyntax(),
+    new LineBreakSyntax(),
     new LinkSyntax(),
     new ImageLinkSyntax(),
     // Allow any punctuation to be escaped.
@@ -29,10 +30,6 @@
     new TextSyntax(r'&', sub: '&amp;'),
     // Encode "<". (Why not encode ">" too? Gruber is toying with us.)
     new TextSyntax(r'<', sub: '&lt;'),
-    // Escaped newlines become hard line breaks.
-    new TextSyntax(r'\\\n', sub: '<br />\n'),
-    // Two or more spaces at the end of a line become hard line breaks.
-    new TextSyntax(r'  +\n', sub: '<br />\n'),
     // Parse "**strong**" tags.
     new TagSyntax(r'\*\*', tag: 'strong'),
     // Parse "__strong__" tags.
@@ -191,6 +188,17 @@
   bool onMatch(InlineParser parser, Match match);
 }
 
+/// Represents a hard line break.
+class LineBreakSyntax extends InlineSyntax {
+  LineBreakSyntax() : super(r'(?:\\|  +)\n');
+
+  /// Create a void <br> element.
+  bool onMatch(InlineParser parser, Match match) {
+    parser.addNode(new Element.empty('br'));
+    return true;
+  }
+}
+
 /// Matches stuff that should just be passed through as straight text.
 class TextSyntax extends InlineSyntax {
   final String substitute;