Move monitors and primary_monitor functions into Glfw::Monitor

Makes more sense for them to be there rather than under Glfw.
Fix GLFW 3 link.
Fix typo in joystick_present name.
Rename 'joystick_present' to 'joystick_present?'
Document functions. Add unset_context.
Implement rb_glfw_swap_interval and rb_glfw_extension_supported.

Not sure how I missed those, but okay.
Add set_position and set_size.

resize and move will still remain, though they'll be more like aliases
for now (though it's possibly to override one and not the other).
Update gemspec.

Include license and readme with the gem. Also some rdoc settings.
Document ruby source.
Version 0.2.0

Increment minor version.