improve code readability
improve code readability
2d camera feature, fix bug sprite visibility

and improve code readability too
rename Visibility to Occlusion, code readability

some people invented this technique, and called it Occlusion, so i
should not create a new stupid name.
create ofxBitmapFont

and add some method headers to ofxSpriteText
add some method headers to ofxSpriteText

and grouping source files