Standardized button names, reworked mapping lookup, API changes
* button and axis names are standardized, no gamepad specifics
* mapping definition has been reworked to a more compressed form
* mapping lookup has been refactored to allow any filter combination
* dropped a few extra mappings due to standard mapping compliance
* API changes:
** dropped UNSUPPORTED event, definition marked deprecated (all are supported)
** removed public references of 'mapping' - both in events and gamepad object (no public use of it)
* Workflow changes:
** dropped buttonsDown member of gamepad - state can be determined via lastState
** _update() does not parse mapping anymore, all compiled at _connect()
Merge pull request #15 from dertseha/standard_names

Standard names for buttons & axes, reworked mapping mechanism