add Image class
add texture filters to constructor parameters
add NullSurface class
add texture filters to texture constructor parameters
add Image constructor and Image version for drawImage
change constructor's data parameter to const
update README.md
add texture filters to constructor parameters
change bitmap to premultiplied alpha, constructor data parameter to const, add Image constructor, add initial version of gradient
add class Path
add arcTo method
fix AddArc usage
fix arc, add getCurrentPoint