New:

• Add LESS support.
• Add empty icon state using empty. (it will make icon disappear).

Improvements:

• Fix icon transition from angel to angle-double.
• Fix icon transition from sort to sort-half.

18 new icons:

• circle-minus
• circle-plus
• circle-times
• circle-o
• circle-o-filled
• circle-o-minus
• circle-o-plus
• circle-o-times
• square-minus
• square-plus
• square-times
• square-check
• square-o
• square-o-filled
• square-o-minus
• square-o-plus
• square-o-times
• square-o-check