Changes

twjit: add underrun extension feature

Themyscira Wireless RTP jitter buffer implementation (twjit) was
originally designed for continuous streaming, as opposed to RTP
streams with intentional gaps.  However, intentional gaps in the
case of DTX pauses or radio errors are called for by 3GPP AoIP
specs and are the default mode for UL RTP Tx in OsmoBTS - therefore,
this philosophical incompatibility between twjit and RTP intentional
gaps is likely to be an obstacle to the desired replacement of
Belledonne ortp with twrtp+twjit in OsmoBTS.  The greatest practical
effect of this philosophical mismatch occurs with RTP streams that
apply intentional gaps for DTX: with standard twjit algorithm,
isolated-island comfort noise update packets throughout each DTX
pause will be dropped.

Underrun extension is an optionally-enabled modification to twjit
algorithm that solves the problem of isolated-island CN update
packets during DTX pauses - i.e., delivers these packets to the
application on the output side of twjit.  As detailed in the
included document update, this solution is not perfect in that
these isolated CN update packets will be delivered only in steady
flow state but not in new flow acquisition states - but it is the
best solution this author can currently provide for the problem of
RTP intentional gaps.

Related: OS#6474
Change-Id: Ibda74c0dbfb163f5d0e3fb13f593a6e2c6817673

gitignore: ignore generated .wasm files

Change-Id: I023158cc39989d6fe98080fecb61410aa4e535ab