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.
Make it so --msglevel extends previous --msglevel uses, instead of
overwriting them. Do this by literally appending the --msglevel option
value to the previous one.
Always pass around mp_log contexts in the option parser code. This of
course affects all users of this API as well.
In stream.c, pass a mp_null_log, because we can't do it properly yet.
This will be fixed later.
Basically, reimplement --msglevel. Instead of making the new msg code
use the legacy code, make the legacy code use the reimplemented
functionality.
The handling of the deprecated --identify switch changes. It temporarily
stops working; this will be fixed in later commits.
The actual sub-options syntax (like --msglevel-vo=...) goes away, but I
bet nobody knew about this or used this anyway.
Since m_option.h and options.h are extremely often included, a lot of
files have to be changed.
Moving path.c/h to options/ is a bit questionable, but since this is
mainly about access to config files (which are also handled in
options/), it's probably ok.
