Add property for custom NSNumberFormatter

Also deleted a few extra spaces in the comments
Modify -countForSegmentAtIndex:

Enable use of custom NSNumberFormatter
Modify -setCount:forSegmentAtIndex:

Enable use of custom NSNumberFormatter
Add -setNumberFormatter: method
Change return type of initializer to instancetype
Add private property to hold counts
Remove extraneous synthesize lines
Add line to initialize counts property
Refactor -countForSegmentAtIndex:
Refactor -configureButtonForSegment:
Modify -setCount:forSegmentAtIndex:

Moved most of the work to -configureButtonForSegment:
Add more documentation to numberFormatter property
Corrected -didSelectedButton: method name
Code re-structure and fixes a few bugs after the ndmeiri’s additions
Fixes #23
Updates sample project