Fixed text color-change glitch

If the text color of the label changes, the animated characters will stay the original color during animations.  During the attribution stage, the current color of the text is applied to the attributed text so that that the animated changes are the correct color.
Completion Block added
Merge branch 'master' of https://github.com/waynehartman/TOMSMorphingLabel into waynehartman-master
override `setTextColor` to adapt attribution stages properly according to new text color.
Merge branch 'waynehartman-master'
Merge branch 'master' of https://github.com/cyril94440/TOMSMorphingLabel into cyril94440-master
made use of `setText:withCompletionBlock:` within the simpler `setText:`; renamed the completion block to be more descriptive;
Merge branch 'cyril94440-master'
bumped version to 0.2.5; added documentation for completion block;