Addition of detectors which skip first few frames
of audio before they start to process it helps
to properly handle some Verizon voicemails.
The result of avmd test using this commit is
OK. All PASS [100]

Thi scommit also resolves:
FS-9588 Add script for outbound avmdy
FS-9589 Add resolution info to events

Now avmd detection is done in detector threads
processing audio frames with different resolution
and/or offsets. Detection decision is based on relative
standard deviation which dynamically adjusts to the signal.
Detection of amplitude, frequency and both simultaneously
is enabled and corresponding setting added to the configuration.
Frequency estimates are filtered with median filter.

This commit also resolves:
FS-9539 - Get estimates with different resolution
FS-9513 - Use adjustable thresholds
FS-9502 - Add detection mode setting
FS-9501 - Enable three modes of detection
FS-9407 - Add check of amplitude for NaN before appending to SMA buffer
FS-9139 - Unit test framework

Merge pull request #968 in FS/freeswitch from ~DINGDING/freeswitch:bugfix/FS-9536-fix-switch_core_hash_delete-return-invalid to master

* commit '9f01830d':
  FS-9536 [core] fix return value

FS-9525 #resolve [Client initiated REINVITE with different audio codec into conference causes choppy audio]

Merge pull request #970 in FS/freeswitch from feature/FS-9543-add-pre-exec-state-change-hooks-to to master

* commit '6a064a95':
  FS-9543 #resolve [Add pre-exec state change hooks to core]

* commit 'e76350df':
  FS-9526 [mod_conference] add deaf sounds

Merge pull request #967 in FS/freeswitch from ~PIOTRGREGOR/freeswitch:bugfix/FS-9527-freebsd-10.3-compile-error to master

* commit '0247c92c':
  FS-9527 [avmd]: Fix MAP_POPULATE on FreeBSD

Remove unsupported flag.

* commit '1c00e64a':
  FS-9533 [mod_conference] add member-enter-sound

Merge pull request #960 in FS/freeswitch from ~SJTHOMASON/freeswitch:bugfix/FS-9424-__byte_order-macro-not-defined-correctly to master

* commit '0c9ab17c':
  FS-9424: Make big endian ifdefs more specific

* commit '03e87faa':
  FS-9518 [mod_conference] allow deaf only command in caller-controls

Merge pull request #959 in FS/freeswitch from ~PIOTRGREGOR/freeswitch:feature/FS-9519-avmd-test-script to master

* commit '8f495672':
  FS-9519: [avmd] Add unit test

Add perl script for testing of voicemail detection.

Merge pull request #950 in FS/freeswitch from ~SJTHOMASON/freeswitch:bugfix/FS-6954-freeswitch-adds-additional-m-audio to master

* commit 'd5b5e8c2':
  FS-6954: Use channel flags to check for proxy media or bypass media

Merge pull request #929 in FS/freeswitch from ~PIOTRGREGOR/freeswitch:feature/FS-9138-avmd-copy-xml-config-to-confdir to master

* commit 'c304eaf3':
  FS-9138: [avmd] Add config to vanilla folder

* commit '0fddb6b0':
  FS-9505 [mod_conference] honor verbose-events in conference-create event

Merge pull request #954 in FS/freeswitch from ~PIOTRGREGOR/freeswitch:feature/FS-9509-subscribe-to-avmd-messages-script to master

* commit '194a2485':
  FS-9509: [avmd] Add perl script subscribing to avmd events

The script will subscribe to avmd events and output them to the console.