Remove unused LED_MODE enum.
New get_error_msg API returns const char *
Help from @blakejohnson to simplify aps2_call macro using splatting
Change to enumerate_APS2s to not clobber Base.enumerate
Convert over trigger API to APS2_STATUS.

Be explicit about TRIGGER_SOURCE enum at top level.
Bump MAX_WF_LENGTH to 128kS
Convert waveform loading to APS2_STATUS

See http://www.boost.org/doc/libs/1_50_0/libs/bind/bind.html#err_overloaded for why we had to cast the function before binding.