This basically reuses the scripting infrastructure.
Note that this needs to be explicitly enabled at compilation. For one,
enabling export for certain symbols from an executable seems to be quite
toolchain-specific. It might not work outside of Linux and cause random
problems within Linux.
If C plugins actually become commonly used and this approach is starting
to turn out as a problem, we can build mpv CLI as a wrapper for libmpv,
which would remove the requirement that plugins pick up host symbols.
I'm being lazy, so implementation/documentation are parked in existing
files, even if that stuff doesn't necessarily belong there. Sue me, or
better send patches.
And replace the sort-of duplicated explanations.
(It's a bit funny to use weblinks to the generated web version of itself
instead of proper RST links, but I think I don't care.)
