add alpha support
add alpha support

GerHobbelt/TinyColor,GerHobbelt/TinyColor,weepy/TinyColor,mwcz/TinyColor,pandabamboo90/TinyColor,pandabamboo90/TinyColor,dabassett/TinyColor,mwcz/TinyColor,bgrins/TinyColor,bgrins/TinyColor,dabassett/TinyColor,vxvinh1511/TinyColor,vxvinh1511/TinyColor,weepy/TinyColor