Move keyboard simulation code to accessibility_keyboard

And depend on the gem.
Make sure ScrollArea.rb explicitly loads mouse

Since it depends on mouse.
Remove the C extension metainfo from the gemspec
Update documentation strings in the gempspec
Update homepage in the gemspec
Remove obsoleted rake tasks and dependencies
Add type documentation for the KAX constants on MRI
Fix initialization of Accessibility.debug on MRI

Since MRI doesn't have the same "feature" related
to metaclasses that MacRuby does.
Enable AXDEBUG by default when running the console