Add flag to disallow half-integral ratings

We don't allow ratings of 0.5, 1.5 etc
So I added a flag (with the same default behaviour as current)
Merge pull request #1 from neilkimmett/master

Initialize gestures in separate method (for IB)
Fix stars not being horizontally centered

Shout out to @pipt for noticing
Alignment before: http://cl.ly/image/0S3L0Z370N15/Screen%20Shot%202014-08-01%20at%2009.27.41.png
Alignment after: http://cl.ly/image/292A3D1p3W38/Screen%20Shot%202014-08-01%20at%2009.32.18.png
Merge pull request #2 from neilkimmett/add-half-integral-flag

Add flag to disallow half-integral ratings
Merge pull request #3 from neilkimmett/fix-horizontal-alignment

Fix stars not being horizontally centered