Support large req body.
Allow set body handler.
Use type mbuf for body parameter.

Reported-by: Coverity Scan

Adds `__restrict` macro for WIN32

* sip: add UAS authentication

* sip: improve err handling for UAS auth

Fixes also a clang analyzer warning "call argument uninitialized".

* sipsess: fix UPDATE issues

In modify.c:sipsess_update() sess->req containing the original INVITE
request was overwritten with the UPDATE request which could lead to a
multitude of problems.

Now, an UPDATE is sent by allocating a sipsess_request and sending it is
handled separately from re-INVITEs.

* sipsess: UPDATE improvements

Remove unused parameters from sipsess_update and correct conditional
checks in sipsess_modify.

* sipsess: call answer handler for each SDP answer (#2074)

Realtime clock time is useful for calculating NTP time points for
RTCP SRs. Applications may use this function to associate RTP
timestamps of sent RTP packets with realtime clock time points,
so that this association is subsequently used to calculate NTP time
points in RTCP SRs.

Obtain the wallclock time once and convert it to both NTP and RTP timestamps
instead of obtaining the current time twice, separated with a mutex lock.
This improves media synchronization quality.

Also, when no RTP packets have been sent and no reference timestamps are
available, generate RR instead of SR to avoid sending bogus timestamps
in the SR.

The realtime timestamps allow the application to specify the time point
that corresponds to the RTP timestamp on the media presentation timeline.
This can be called "capture time", for whatever definition of "capturing"
the application has.

This timestamp is further used to calculate the NTP/RTP timestamps that
are sent in RTCP SR and used on the receiver to synchronize different
media streams from the sender. Having the timestamp provided by the
application allows for a more precise correspondence between NTP and RTP
timestamps, even if the media is sent non-monotonically and out-of-order.

* ci: convert valgrind to cmake

* valgrind: use cmake build

* valgrind: minor fixes

* valgrind: build rem with cmake

* coverage: enable verbose retest

* ci: migrate to cmake

* run scan-build-14 twice

* cmake: add LINKLIBS and make backtrace and zlib optional

* fix darwin libs

fixes #520

src/pcp/request.c:115:13: warning: Possible null pointer dereference: msg [nullPointer]
 if (err || msg->hdr.result != PCP_SUCCESS ) {
            ^
src/pcp/request.c:141:29: note: Calling function 'completed', 3rd argument 'NULL' value is 0
  completed(req, ETIMEDOUT, NULL);
                            ^
src/pcp/request.c:115:13: note: Null pointer dereference
 if (err || msg->hdr.result != PCP_SUCCESS ) {
            ^

```
src/fmt/print.c:77:15: error: Pointer arithmetic overflow; 'buf' buffer size is 64 [ctuPointerArith]
 char c, *p = buf + NUM_SIZE - 1;
              ^
src/fmt/print.c:272:20: note: Calling function local_itoa, 1st argument is uninitialized
   len = local_itoa(num, (sn < 0) ? -sn : sn, base,
                   ^
src/fmt/print.c:77:15: note: Using argument buf
 char c, *p = buf + NUM_SIZE - 1;
```

A periodic un-REGISTER should be done only if `fbregint` (fallback SIP server
registration interval) was set.

UPDATEs are now sent with Contact header which is mandatory according to
RFC 3311.