Grunt API usage for replacing two modules

Replaced `mkdirp` and `glob` with Grunt API usage, thus closes #19 and #20.

Small configuration changes, due to using Grunt API `options` which simplifies the plugin and makes it easier to continue working on #13 and #10 as well as multi task usage #12.

It is a work in process, but would like to have it reviewed and possibly merged as it already brings improvements.