Use NSHashTable instead of NSOrderedSet to store checkBoxes weakly

Merge pull request Boris-Em#46 from Boris-Em/feature/offColor

Add new offFillColor property.

Merge pull request Boris-Em#29 from andrey-krukovskiy/CarthageSupport

Carthage support

Merge pull request Boris-Em#19 from xinsight/increase-touch-area

increase touch area if checkbox is smaller than 44pt

Merge pull request Boris-Em#12 from WangHengHeng/master

Fix Boris-Em#13,  Square checkbox of size less than 20 x 20 px appears distorted.

Fixes bug Boris-Em#2 - Check box will be hidden If on property is tru…

…e by default. Boris-Em#2

Added delegate section

Added image