Modify parser to group html begin/end elements.

- Added a "Tag" block type.
- Wrapped all begin/end elements in a "Tag" Markup block.

#75

Since this impacted a large amount of the existing tests I've created a separate "test" PR.  I felt that the existing tests did more than enough verification for this "feature" since it's at the core of the Razor parser, let me know if you have a different opinion.

Test PR: