Proposed changes as we move to a v1.0.0

This major refactor includes the following:
* Use grunt 'options' properly
* Use src/dest
* Support for per-file file extensions
* Partially updated documentation

It does not (yet) include:
* Full test suite
* Fully updated documentation

You can see an example project using the new parameters at: https://github.com/kengoldfarb/grunt-swig-test
Can sitemap.xml be configurable? Might be good to move this string literal to config.