Language Specification in Markdown format

Fixes #213.

This pull request adds the language specification in Markdown format.

The pull request also includes a tool (word2md) that can convert Word documents to Markdown format. The tool uses the Word Automation APIs to start an instance of Word and access the contents of the document being converted. The tool must be run using the cscript.exe script host and requires Word to be installed on the target machine. The tool recognizes the specific Word styles used in the TypeScript Language Specification but could easily be adapted to other uses.