pipe-win32: possible fix for Windows XP deadlock

This fixes a hang with the VirtualBox OpenGL drivers. It might help
with #1325 as well.
DOCS/contribute.md: remove unintentional headline

The # from the IRC channel made it appear as a headline.
options: make --no-... options work for OPT_REPLACED too

Do this by automatically adding the option, if the aliased option name
also has a "no-..." variant.

Could be easier by manually adding "no-..." variants to the option list,
but this seems better because you can't just forget it.
demux: don't always make --cache-secs override --demuxer-readahead-secs

It's confusing. Whether the new behavior is less confusing... whatever.
command: add properties for current bitrate

Fixes #1192.
DOCS/crosscompile-mingw: update

Unrecommend mingw-w64-cmake, point out MXE host requirements.
Check some mallocs

Fixes #1337.
options: fix parsing for --ab-loop-*

Editing mistake. Oops.
player: add a --keep-open=always mode

The --keep-open behavior was recently changed to act only on the last
file due to user requests (see commit 735a9c39). But the old behavior
was useful too, so bring it back as an additional mode.

Fixes #1332 (or rather, should help with it).
options: add option for ignoring patch in resume mechanism

Whatever.

Fixes #1281.