Optimize grunt tasks

As discussed in #57 we needed a solution to avoid annoying merge conflicts of the minified file whenever several PR's are simultaneously outstanding.

I simply split the testing part into its own task. Easiest for now is that contributors run `grunt` which aliases to `grunt test` and leave the building to you, once you've merged the PR.
I've no idea how other libs handle the minified/binary files, except by leaving them out of the repo altogether.

As far as I'm concerned all my PR's can be merged, unless I missed something?