Should fix a compile-time error on simulator.

Change-Id: I5962479579350ebffe6dcce4f65a629b108ff936

Derivative of work by RobertGabrielJakabosky
 http://lua-users.org/wiki/EmergencyGarbageCollector

I've only implemented the not enough memory part and
 expanded this idea to adding a mechanism to signal
 the OOM condition of the plugin buffer which allows us to only
 grab the playback buffer after garbage collection fails
 (SO THE MUSIC KEEPS PLAYING AS LONG AS POSSIBLE)

Change-Id: I684fb98b540ffc01f7ba324ab5b761ceb59b9f9b

Change-Id: I04bc38d03b7f0ca65a815685eb6ab0f5ff825c45

add defines for sound functions
 SOUND_VOLUME, SOUND_BALANCE, SOUND_CHANNELS, SOUND_STEREO_WIDTH ...
 defines depend on target
 require "sound_defines" to add them to rb.sound_settings[]

consolidates:
 sound_set, sound_current, sound_default, sound_min, sound_max,
 sound_unit, sound_pitch, sound_val2phys to a single function

 rb.sound("name", setting, [value])

 require "sound.lua" for old functionality

Change-Id: Ice695218aa433f4fcbb48fbd6b8a9bf29c994110

This library allows events to be subscribed / recieved within a lua script
most events in rb are synchronous so flags are set and later checked by a
secondary thread to make them (semi?) asynchronous.

There are a few caveats to be aware of:

FIRST, The main lua state is halted till the lua callback(s) are finished
 Yielding will not return control to your script from within a callback
 Also, subsequent callbacks may be delayed by the code in your lua callback
SECOND, You must store the value returned from the event_register function
 you might get away with it for a bit but gc will destroy your callback
 eventually if you do not store the event
THIRD, You only get one cb per event type
 ["action", "button", "custom", "playback", "timer"]
 (Re-registration of an event overwrites the previous one)

Usage:
 possible events =["action", "button", "custom", "playback", "timer"]

 local evX = rockev.register("event", cb_function, [timeout / flags])
  cb_function([id] [, data]) ... end

 rockev.suspend(["event"/nil][true/false]) passing nil affects all events
  stops event from executing, any but the last event before
  re-enabling will be lost, passing false, unregistering or re-registering
  an event will clear the suspend

 rockev.trigger("event", [true/false], [id])
  sets an event to triggered,
  NOTE!, CUSTOM_EVENT must be unset manually
  id is only passed to callback by custom and playback events

 rockev.unregister(evX)
  Use unregister(evX) to remove an event
  Unregistering is not necessary before script end, it will be
  cleaned up on script exit

Change-Id: Iea12a5cc0c0295b955dcc1cdf2eec835ca7e354d

Rockbox constants are auto generated by a perl script like the majority
 of the plugin functions.

Constants are contained in rb_defines.lua, if the file exists it is auto loaded
 by the lua state for backwards compatibility

Frees ~1k

Change-Id: I237700576c748f468249e501c839d89effca3f39

Allows saving of ram by reusing strings already stored in the binary
and storing a pointer instead of malloc and copy to get them inside
the lua state

Saves about 1.5K overall

Derivative of work by bogdanm
RAM optimizations: pseudo RO strings, functions in Flash
https://github.com/elua/elua/commit/d54659b5723bcd2b1e3900362398c72c18a9aa0b

Change-Id: I21d6dcfa32523877efd9f70fb0f88f2a02872649

track elapsed is needed to use fast-forward and rewind effectively
track length might as well be added too..

Change-Id: I906c92eb5260164c6177d8c0a8ff879b1fad7898

moved items to rb.system
added read access to audio_current_track and audio_next_track

Change-Id: Ia055b8cb3848e540067818f596ffd1058da057fb

Change-Id: Ibe2bc6602ff27524a3b96d9523780acbfbf03c76