Add PlastiCSS core

Add useful functions for numbers:
+ removeUnit

lists:
+ inList
+ last
+ slice
+ splice

And a function to easily add credits for PlastiCSS and vendor modules in the css:
+ credits
Revert "Add PlastiCSS core"

Add useful functions for numbers:
+ removeUnit

lists:
+ inList
+ last
+ slice
+ splice

And a function to easily add credits for PlastiCSS and vendor modules in the css:
+ credits
Make change to rem module and add font module
Add support for entypo, fontAwesome and iconic icon fonts
Add a config file exemple