initial POPAnimator thread safety
Merge branch 'master' of https://github.com/RuiAAPeres/pop into RuiAAPeres-master
Merge branch 'RuiAAPeres-master'
Add barTintColor Animatable Property
Add barTintColor Animatable Property

POPAnimatableProperty.h
add support for platform-specific colors; issue #39
add more external resources
Merge branch 'master' of https://github.com/nicopasso/pop into nicopasso-master
Merge branch 'nicopasso-master'
add color interpolation to basic animation; fix #36