Update devel/ruby-SDL to 2.1.1.

* Use lang/ruby/gem.mk instead of misc/rubygems/rubygem.mk.
* Add LICENSE.
* Remove default value of GEM_BUILD.

version 2.1.1
Fix a compile problem on MacOS X
Rename sdl.so to sdl_ext
Add following constants
* SDL::Mixer::NO_FADING
* SDL::Mixer::FADING_OUT
* SDL::Mixer::FADING_IN
* SDL::TRANSFORM_AA(for compatible with 1.x)
* SDL::TRANSFORM_TMAP(for compatible with 1.x)
* SDL::TRANSFORM_SAFE(for compatible with 1.x)
Fix documents
Remove obsolete documents

version 2.1.0
add following methods
* SDL::TTF#close
* SDL::TTF#closed?
* SDL::BMFont#close
* SDL::BMFont#closed?
* SDL::Kanji#close
* SDL::Kanji#closed?
* SDL::Surface#destroyed?
* SDL::Joystick#closed?
* SDL::Mixer::Wave#destroyed?
* SDL::Mixer::Music#destroyed?
* SDL::Kanji#get_coding_system
modify documents
Async following methods on Ruby 1.9
* SDL::Event#wait
* SDL.delay
Ruby m17n support on Ruby 1.9
* SDL::WM.set_caption
* SDL::WM.caption
* SDL::TTF#draw_solid
* SDL::TTF#draw_blended
* SDL::TTF#draw_shaded
* SDL::TTF#render_solid
* SDL::TTF#render_blended
* SDL::TTF#render_shaded
* SDL::Kanji#put
* SDL::Kanji#putTate
* SDL::SDLSKK#str
Fix the bug of following methods
* SDL::MPEG#move

version 2.0.1b
fix sample bug
fix SDL::MPEG.info

(taca)