added no-warning-comments rule

squashed commits:
* added no-warning-comments rule
* extended documentation with some examples
* warningTerms are no longer passed as they are already in the context
* rule is now configured with an additional configuration object
* extended and rearranged documentation for no-warning-comments rule
* added JSDoc comments
Merge pull request #671 from lusini/add-no-warning-comments

Added no-warning-comments rule (fixes #660)
Merge pull request #708 from michaelficarra/GH-699

fixes #699: brace-style does not check function expressions
fixes #711: eslint reports wrong line number for files with shebang

I also took the liberty of moving the shebang stripping to lib/eslint.js
so it is supported through the API, not just the CLI. Same test should
cover both.