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.

change build dependencies so that (cross) compile and gem tasks no longer need the explicit configure task

add tasks for downloading and cross compilation of libfox, fxscintilla and depending libraries for win32

By default it looks like rake-compiler doesn't modify the gem spec
appropriately when we're cross-compiling for multiple Ruby versions.
Added some lines to remove "lib/fox16.so" from the gem spec's list
of files to include, and then added "lib/1.8/fox16.so" and "lib/1.9/fox16.so"
back to the list, so that we get the correct result.

Followed the instructions at http://github.com/luislavena/rake-compiler
to modify the ExtensionTask so that it supports cross-compilation. This
included moving the 'config_options' that were being used for a
RUBY_PLATFORM of "mingw" into the new 'cross_config_options' parameter.

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).