Add functionality to mark options that depend on features disabled at
compile time as disabled rather than not compiling the option
definitions at all. This allows printing a warning about the option
not being available because of a disabled feature, instead of just
"unknown option". Because the option definitions are still compiled
fully, this only works for definitions that do not reference symbols
which are not available if the feature is disabled. Use the new
functionality for options depending on libass.
Command line options like "-foo xyz" are ambiguous: "xyz" may be a
parameter to the option "foo" or an unrelated argument. Instead of
relying on the struct m_config mode field (commandline/file) pass
parameters to specify ambiguous mode explicitly. Meant for "--foo"
options which are never ambiguous on command line either.
The global was used in the function cfg_include which handles the
-include option. Make the address available in that function by
creating a new dynamically allocated option in m_config_new that has
the address in the option's private data.
asxparser.c also used the global. Making it available through all ways
the code could get called required a number of relatively straightforward
changes to playtree and menu code.
First part of option restructuring. The aim is to move option values
from a huge number of separate globals to a single non-global struct.
This part adds some support for parsing option values into such struct
instances, and moves one example option (fixed-vo) to the struct.
