Changes from gsm-codec-lib-r3 to gsm-codec-lib-r4:

* Libgsmfr2 evolved from version 2.0.0 to version 2.1.0: see
  doc/FR1-library-history for the details.

* Libgsmefr evolved from version 1.1.0 to version 1.2.0: see
  doc/EFR-library-history for the details.

* Command line utilities support the new hexadecimal file format of TW-TS-005
  Annex A for FR and EFR codecs (see doc/TW-TS-005 article):

  + tw5a-dump parses TW-TS-005 Annex A files in the same way how gsmrec-dump
    parses gsmx binary files;

  + gsm[e]fr-decode-tw5[-r] are new speech decoder utilities that read their
    input from TW-TS-005 Annex A files;

  + gsmx-to-tw5a and tw5a-to-gsmx conversion utilities should be sufficient for
    most other use cases.

* New command line utility gsmfr-tfo-xfrm exercises TFO transform addition to
  libgsmfr2.

Changes from gsm-codec-lib-r2 to gsm-codec-lib-r3:

* Libgsmfrp has been replaced with libgsmfr2, a major version change per SemVer.

* The former dependency on historical libgsm has been eliminated; the
  functionality of libgsm (GSM 06.10 encoder and decoder implementation) has
  been absorbed into libgsmfr2.

* Libgsmefr version 1.1.0 exhibits approximately 2x performance improvement
  over the original version, and also exhibits a small addition to the public
  API: the RTP-encoded form of the standard EFR DHF is now provided as a const
  datum.

* New library added: libtwamr for 3GPP AMR-NB codec, serving as a replacement
  for libopencore-amrnb in Themyscira GSM codec exploration workflows.

* New command line utilities:

  + amrefr-* and twamr-* related to libtwamr: see doc/Codec-utils,
    doc/AMR-EFR-hybrid-emu and doc/AMR-library-tests articles.

  + amrts-pcm8-compact: see doc/Utils-overview article.

  + gsmfr-* updates for libgsmfr2: see doc/Codec-utils article.

  + gsm[e]fr-dlcap-sync: see doc/Calypso-TCH-downlink article.

* gsmfr-* utilities set: gsmfr-hand-test and gsmfr-max-out hack programs have
  been dropped.  These hack programs were never properly documented and were
  written only as part of a debug chase, in pursuit of a bug that ultimately
  turned out to be in our then-hacky patch to osmo-bts-sysmo.

* gsmrec-dump now prints the bit-counting SID classification for both FRv1 and
  EFR codecs, and also identifies bit patterns that match the official DHF
  (decoder homing frame) for each codec.

* The configuration and build process has been revamped: the full suite of
  libraries and utilities can now be installed in any desired file system
  location without contortions.

Changes from gsm-codec-lib-r1 to gsm-codec-lib-r2:

* Libgsmfrp evolved from version 1.0.0 to version 1.0.2; please see
  doc/FR1-Rx-DTX for a detailing listing of libgsmfrp changes.

* Some new utilities have been developed for studying AMR: see
  doc/AMR-study-utils for more information.

* The subject of conversions between 16-bit 2's complement linear PCM and 8-bit
  A-law and mu-law PCM formats (G.711) has been thoroughly studied, the findings
  have been documented in doc/PCM8-conversions, and some new command line
  utilities have been added, described in the same article.

* Many new table generators have been added to the dev subdirectory; some of
  them may be useful to other software developers.

* pcap utilities have been split off to a separate rtp-debug-utils repository;
  this split was made so that those utilities can be developed freely while the
  gsm-codec-lib repository remains under strict release process control.