Update README instructions
Adhere to colon separations between prop/val Stylus style convention
Convert padding variable to pad as Stylus style convention
Remove image from edit() mixin as Stylus lib ver of Jeet won't support
Convert all @extends to @extend for the sake of consistency
Make center() mixing pad = 0 by default
Add CHANGELOG.md
Remove files not essential to Stylus library ver of Jeet