Updated to use the new target framework in project.json
Updated build.cmd
Fix nested tags in script tag.

#115
Test nested tags in script tag fix.

#115
Add TagHelper registration system.

- This registration system accepts tag descriptors that it then uses to feed requests for tag helpers.
- Added some infrastructure pieces that are used to build up valid tag helper descriptors.

#70
Validate Tag Helper registration system functionality.

- This involved adding tests to cover GetTagHelpers methods on the default tag helper descriptor provider.

#70
Add TagHelper parse tree visitor.

- The visitor looks for TagBlock's that match registered TagHelpers and rebuilds them into TagHelperBlock's.
- Added the code generator and corresponding chunk for a TagHelperBlock.
- Added syntax tree specific objects & helper methods to create accurate tag helper structures.

#71
Addressed left over code review comments.
Rebased and addressed some code review comments.