Added five browser buttons: chrome, firefox, safari, opera, ie
Resized the browser icons to better fit in the button
Updated preview and readme files
Optimized images with imageOptim
Darkened the white background (from #f8f8f8 to #f4f4f4) for better contrast with hover state and on a white background
Use percentage values for border-radius, height and width values (not bordered round)
Darken the inner border on hover, focus and active states
Updated preview & readme to latest changes
Added seperate mixins file
Updated readme and preview to v.2.1.0
Merged v.2.1 into Master