Adding a build api.
For interoperability purposes, have the build API explicitly declare a current working directory. Revert to previous cwd on exit.
Simplify context issue by first setting a new cwd, then requiring grunt. This scopes grunt to the Modernizr directory and avoids manipulating upstream context.
Remove exit, it can cause upstream processes to bail too soon.
Adding tests for programmatic API.
Adding documentation for API.
Updating syntax.
Merge pull request #967 from doctyper/feature/build-api

Programmatic API
Corrected metadata typo in `cssmask` detect
Merge branch 'master' of https://github.com/Modernizr/Modernizr