+: Added prefixer mixin that we can use in other mixins and classes.
+: Changed two mixins to make use of the new prefixer mixin.
-: Removed autoprefixer from gruntfile, doesn't interfer with prefixer.
+: Made prefixer default to include three most common prefixes

I didn't include -ms, since afaik it's usually absent in the most common
usage cases where we need multiple prefixes.
Merge pull request #3 from redrohX/prefixer

A prefixer mixin we can use

We discussed about this and this is awesome super duper.