Refactored error handling mechanisms for parsing.

- This is needed to make passing error handling devices into more pieces of the parser easy.

#210
Delete trailing whitespace
- #EngineeringDay
- Total replaced: 506  Matching files: 118

Did not change any files under test/Microsoft.AspNet.Razor.Test/TestFiles
- avoiding need to redo hashes
Apply VS' FormatDocument and RemoveAndSort to all *.cs files
- #EngineeringDay

Did not change any files under test/Microsoft.AspNet.Razor.Test/TestFiles
- avoiding need to redo hashes
Add xml-docs-test target to end of default build
- #EngineeringDay
- correct a couple of XML doc issues in the repo
Add missing license headers
- #EngineeringDay
- skip generated files such as Resources.Designer.cs and files under
  test\Microsoft.AspNet.Razor.Test\TestFiles\CodeGenerator\CS\Output
Changed TagHelper attributes to be SpanKind.Code if not string typed.

- Also added tests to validate that non string TagHelper attributes inherit the SpanKind.COde behavior.
- Removed a block wrapping around single markup spans.
Addressed code review comments.