libgsmhr1 RxFE: store CN R0+LPC separately from speech In the original GSM 06.06 code the ECU for speech mode is entirely separate from the CN generator, maintaining separate state. (The main intertie between them is the speech vs CN state variable, distinguishing between speech and CN BFIs, in addition to the CN-specific function of distinguishing between initial and update SIDs.) In the present RxFE implementation I initially thought that we could use the same saved_frame buffer for both ECU and CN, overwriting just the first 4 params (R0 and LPC) when a valid SID comes in. However, I now realize it was a bad idea: the original code has a corner case (long sequence of speech-mode BFIs to put the ECU in state 6, then SID and CN-mode BFIs, then a good speech frame) that would be broken by that buffer reuse approach. We could eliminate this corner case by resetting the ECU state when passing through a CN insertion period, but doing so would needlessly increase the behavioral diffs between GSM 06.06 and our version. Solution: use a separate CN-specific buffer for CN R0+LPC parameters, and match the behavior of GSM 06.06 code in this regard.

libgsmefr change history: version 1.1.0 to version 1.2.0
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* New convenience wrapper function EFR_decode_rtp(): takes RTP input (payload
  bytes and length), encapsulates the logic of TW-TS-001 for both basic and
  extended RTP formats, calls EFR_decode_frame() or EFR_decode_bfi_nodata()
  as appropriate.

* Sizes of internal state structures are exported as public const "variables"
  (const memory words really), allowing alternative methods of allocating memory
  for these structs besides the standard malloc-calling EFR_encoder_create()
  and EFR_decoder_create() functions.

libgsmefr change history: version 1.0.0 to version 1.1.0
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* Performance improvement of approximately 2x;

* A small addition to the public API: the RTP-encoded form of the standard EFR
  DHF is now provided as a const datum.