Include relative path in name

If includePath is true, this will include the relative path to the
source haml in the automatically generated name.

Example:
window.HAML['path/to/haml'] = ... # includePath true
window.HAML['haml'] = ... # includePath false

Add pathRelativeTo option

This option is the basis of the relative path added to name.
Lowercase gruntfile.
Merge branch 'include-relative-path-in-name' of https://github.com/leahciMic/grunt-haml into leahciMic-include-relative-path-in-name
Rename wrapHtmlInJs option to precompile (and invert logic).
Add option docs.
This is defined for haml-coffee.
Make linter happy.
Update README.