Modify parser to group html begin/end elements.

- Added a "Tag" block type.
- Wrapped all begin/end elements in a "Tag" Markup block.
- Attempted to change as little as possible in the parser since it is easily the most fragile part of Razor.

#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: https://github.com/aspnet/Razor/pull/87
It's poor naming, just utilizing what was already there and following the same pattern as the rest of the parser.  Essentially what optional does is verify that we're at a CloseAngle and we're not at the end of the file.  If so, accept it.

Sooo by having this optional like this we can avoid several ```if(!EndOfFile)```