[ffigen] Added large tests, bug fixes (#33)

closes #29, closes #17

- Added large tests for Libclang, cJSON and SQLite #17.
- Bug fix: Nested parsing, added tests for nested parsing. Sub parsers now use a stack to hold information about current declaration.
- Bug fix: Unsupported operation error when finding dynamic library path on windows #29.
- Added property originalName to Binding.
- Config provider now throws ConfigError if a required config is missing. This fixes tests not running previously due to exit call in config provider.
- Updated libclang wrapper to support running from multiple isolates (fixes concurrent test running).