Update version handling
Add Window#icon=
Add some options to testsprite
Cosmetic change
Add Surface.from_string and #pixels
Rename PixelFormat#bps to #bpp
Add Surface#{bits,bytes}_per_pixel
Add test script for Surface class
Update jp documents
Update documents of class Point
Update docstrings of Window.create
Link to COPYING from README.md
How to install Ruby/SDL2
Use markdown for docstrings
Update docstrings
Stop using rb_define_private_method for initialize method
since rb_define_method defines private method for initialize and
yard donesn't handle initialize defined by rb_define_private_method.
Update docstring for Point class
Cosmetic change
Update documents
Update japanese documents