Updated BUTTON_MAP and Gemfile

Uses new button mappings if :usb_driver setting is :tattiebogle

Update Gemfile to use personal ruby-sdl-ffi fork
Fix because additional_params is not available at class level
Change button_letter method to use button_map method
Add trigger support

Adds trigger button handling publishing to trigger_lt and trigger_rt
respectively.

Refactored to clean up magic numbers and extra methods.
Add Mac OS X section for XBox 360 Controller

Added details to get the XBox 360 Controller working on OS X, example
code for trigger events.

Fixed typo and replaced rubysdl gem link with ruby-sdl-ffi link since
it doesn't appear to actually use the rubysdl gem.
Update Gemfile

Remove github link to personal fork
Keeping personal master working until pull requests are taken
Changes Gemfile.lock to reflect latest personal ruby-sdl-ffi github version
Add button_up events

Modified logic to send event on button change, selecting button_* or
button_up_* depending on state.  Previous button events are only sent
on down event, and only button_up_* events are sent when the button is
released.
Adding to available commands to avoid warning messages
Add currently_pressed? command

currently_pressed? takes either a symbol or index value to return that
button's current state.
Updated gem versions
PS3 updated to reflect OS X mappings

Added OS X mappings for PS3 Controller. Changed naming from Tattiebogle
to OS X.
Fix leftover button_letter method calls
Make OS specific binding maps

Change joystick drivers for ps3 and xbox360 controllers to use OS
specific binding maps for buttons and axis.
Merge pull request #6 from mikejford/os-controller-mapping

OS/driver based controller mapping implementation