[Feature Proposal] Button-group, input-group

[reinerBa]

Hi, i made a fiddle to demonstrate my proposal jsFiddle Demo with code

With a few lines of code pico can have button groups and input groups. @lucaslarroche do you want me do put the code in the scss files and documentation and create a Pull request?

[leoherzog]

Love this idea, and your implementation is solid

[prikeshsavla]

+1 Love the idea of having a button group system

[DavidSouther]

Love it, so glad I found this before I went to make it myself!