Fix centerToParent method to set screen pixel integral values

The division is now done with floats, which allows for more accurate
centering as integer division is no longer used, but still maintains
pixel integral results based on the device’s screen scale (to avoid
subpixel rendering).
Removed float specifiers. Added PIXEL_INTEGRAL to the rest of the setters. Replaced duplicated code with functions.
Merge pull request #1 from harlanhaskins/master

Removed float specifiers. Added PIXEL_INTEGRAL to the rest of the setters. Replaced duplicated code with functions.
Fix for Pixel Integral results by @smileyborg. v1.0.1.