Release Name: 2.6

Notes:
== Rubygame 2.6.0

Release focus: Ported to FFI.

=== FFI

Rubygame is now pure Ruby, with no compiled C code. Instead, it uses
Ruby-FFI (or compatible FFI implementations) to directly access SDL
and related libraries. That means:

- It is much easier to install. You can install it directly from
  RubyGems (`gem install rubygame`) on any operating system, and you
  don't need a C compiler or SDL headers.

- It is now possible to use Rubygame on JRuby, and possibly on
  Rubinius.

- Rubygame will be slightly slower than before. But, the hard work is
  still being done by SDL, so the speed decrease is only minor. The
  increased portability and ease of future development greatly
  outweighs the small speed loss.

Despite the major architectural change, Rubygame 2.6 API is meant to
be backwards compatible with Rubygame 2.5 and earlier. If you find an
API incompatibility, you should report it as a bug.

However, there are a few minor incompatibilities that are already known,
and most likely cannot or will not be fixed:

- Surface#flip now needs SDL_gfx to run. Before, it needed only plain
  SDL, but the code for it was too slow when reimplemented in Ruby.

- Rubygame::VERSIONS[:sdl_gfx] now reports [0,0,0] when SDL_gfx is
  available, instead of its real version number. SDL_gfx does not
  currently provide any way to detect its version number at run time.
  (VERSIONS still reports nil when SDL_gfx is not available, the same
  as in 2.5 and earlier.)

=== Fixes

- Fixed: Surface#set_at() now correctly sets the pixel's opacity for
  Surfaces with an alpha channel. If no opacity is given for the new
  color (i.e. only RGB), the pixel will be fully opaque.

  - Note: Due to a long-standing bug, Surface.new cannot create a
    Surface with an alpha channel. Use Surface#to_display_alpha to
    create an alpha-channeled copy of the Surface, or load an image
    file that has an alpha channel already.

- Fixed: Music.load now automatically opens audio if needed. MP3s (and
  perhaps other file types) would fail to load in some circumstances
  if audio was not open.

=== Other Changes

- Rubygame now automatically initializes itself when loaded and cleans
  itself up at exit. So, you no longer need to call Rubygame.init or
  Rubygame.quit in your code (but it won't hurt if you do).

- Added: New sample application, a basic image viewer.
  See samples/image_viewer.rb.

- Added: Documentation listing every keyboard symbol used by Rubygame.
  See doc/keyboard_symbols.rdoc.

- Added: Guide to setting custom load parts for SDL libraries.
  See doc/custom_sdl_load_paths.rdoc.

- Surface#alpha= is now a true alias for Surface#set_alpha. It was a
  separate method before. It can still be used in the same way as
  before.

- Surface#colorkey= is now a true alias for Surface#set_colorkey. It
  was a separate method before. It can still be used in the same way
  as before.




Changes: