7.0.0-alpha6 — bring back life for project

Hi everyone!

Seems like original flexboxgrid was abandoned by @kristoferjoseph, I decided fork and continue develop at my own (probably with contributors).

What is already done:

• added breakpoint xl for 1200px and sm now pointed to 576px (kristoferjoseph#232) like Bootstrap v4,
• fixed .container class and now it works properly and not causing horizontal scroll (kristoferjoseph#254),
• cleaned up from messy structure (kristoferjoseph#249)

flexboxgrid2 right now is alpha6, so if you can test it and fills issues (or PRs!) I'll be very grateful.