Allow multitask creation

This will allow creating of multi task files.

will solve issue:
https://github.com/gyllstromk/grunt-bowerful/issues/7


i also merged all my commits from my previous pull:

https://github.com/gyllstromk/grunt-bowerful/pull/11

that pull solves issues:

https://github.com/gyllstromk/grunt-bowerful/issues/6
https://github.com/gyllstromk/grunt-bowerful/issues/5