Default player is MIDIator player.

If user want to extend Stretto functionality with another player / renderer, can do so, in his own namespace. Stretto global namespace will never collide with it, so making it the default doesn't hurt and makes it simpler.
Implemented playing of instruments, variables
Player now handles layers
Passing pattern to player until #play is called

This is because is not responsibility of the player to store a pattern, but merely to play.
Renamed "pitch wheel" to more appropiate name "pitch bend"
Player handles polyphonic pressure
Player handles pitch bends
Player handles key signatures. Pending test/spec
Refactored player to handle elements independently.

This is to prepare for the concept or "Renderers"
Player handles control changes. TODO: implementation for timing elements
default rake task, gem source
README update
version bump
Merge branch 'master' into gh-pages