build: add flag for inline assembly

This is used to disable inline assembly (useful for old version of binutils
like the one in OpenBSD).
video: fix --brightness etc. options

They were set before the VO was intitialized, which silently failed.
bstr: add bstr_xappend function

Apparently this can be really useful when being paranoid and trying to
avoid too much malloc/realloc, since it can be used to appending into a
buffer (with transparent realloc only if the buffer is too small).
common: simplify and optimize string escape parsing

This code is shared between input.conf parser and option parser. Until
now, the performance didn't really matter. But I want to use this code
for JSON parsing too, and since JSON will have to be parsed a lot, it
should probably try to avoid realloc'ing too much.

This commit moves parsing of C-style escaped strings into a common
function, and allows using it in a way realloc can be completely
avoided, if the already allocated buffer is large enough.
osd_libass: use bstr_xappend()

Partially, just enough to drop mp_append_utf8_buffer().
input: use bstr_xappend()

To get rid of mp_append_utf8_buffer().
bstr: use mp_append_utf8_bstr()

Drop usage of the ugly PUT_UTF8() macro.
common: drop mp_append_utf8_buffer()
manpage: fix vf_noise parameter name
build: check for libatomic and __atomic operations

Add check in old-configure as well. Reformat the check to use a maximum of 80
columns in the wscript.
Signed-off-by: Stefano Pigozzi <stefano.pigozzi@gmail.com>
compat: use __atomic operations instead of __sync, when present

Fixes #434
Fixes #437
Update copyright year
player: fix DVD playback

Crashed in case of lazily added subtitle streams, which add tracks with
track->stream set to NULL.

Fixes gituhub issue #439.
mpv.desktop: Add Czech translations
player: load encoding-profiles.conf before the main config

Otherwise one can't add profiles based on the encoding profiles.
manpage: fix description on the slave mode msglevel
options: make  --msglevel=help print something helpful
manpage: clarifications about bitmap subtitles and --secondary-sid
build: make configure fail if both __atomic and __sync are not available
build: fix typo