strptime: Implement %T, minor cleanups

See merge request !627

* %T is implemented but untested for now (we lack strptime tests)
* I switched some unexported, immutable statics to const as it's a
  better fit
* parse_am_pm() now correctly strips prefixed whitespace AND doesn't
  allocate heap memory

Use C string literals & deprecate `c_str!`

See merge request !625

Few improvements to `time.h`

See merge request !622

Remove obsolete varargs workaround

See merge request !621

fix: cbindgen emits wrong vsscanf signature

See merge request !619

`cbindgen` emits `...` instead of `va_list` when the final parameter is
named `__valist`.

fix: USHRT_MAX is too large

See merge request !618

The original expanded to 16 nibbles which is technically correct because
the standard defines USHRT_MAX as being at LEAST 65535. However, in
practice everything seems to set the max as the max length of two bytes.

Add docs, deprecations for sys/time.h

See merge request !616

Add docs for netinet headers

See merge request !615

Add pvalloc()

See merge request !614

Add docs, missing functions for strings.h

See merge request !611

wscanf and vwscanf implementation proposal

See merge request !613

Fix sigqueue test

See merge request !612

Fix clock_getcpuclockid() parameter type

See merge request !610