Important syntax update

• grid-item instead of `grid__item``
• grid-item--modifier instead of grid__modifier--item

Better readme, leaner code, full mobile-first.

• Use the full power of the SASS 4.4. & operator.
• Kill variable-bloat in widths (much more readable now)
• Remove lap-up in favour of a complete mobile-first default break-point config
• Rename legacy to fallback and visibility to visibility-helper in the config.

Cheers!

Enhanced flex-box supprt

Fundament flex-box just got smarter:

• The flex-box grid will now by default stretch its grid__items to fill the vertical space.
• The --top modifier allows you to revert to align to top on flex-box
• The --even modifier allows you to put in items with arbitrary widths, flex-box aligns them for you automagically.

Happy griddin'!