Static linking all dependent libraries into each ruby version (from
1.8 to 2.2) would blow up the gem to >20MB.

Before commit af543822 loading order of fox16.so and fox16.rb was irrelevant.
But now fox16.rb must be called, in order to load ruby files to the C++
extension. Renaming the C++ extension ensures, that fox16.rb is called first.

determine which shared library to load.

If RUBY_PLATFORM says we're on Windows, this loader will look under
a version-specific directory to try to load the extension. For other
platforms, it will just load the appropriate shared library from
the current directory.

In the interest of keeping this as simple as possible, I've extracted
the source files for the FXRuby User's Guide into a separate project
(fxruby-guide).