vf_vdpaupp: cosmetics: rename function
playlist: fix playlist_move on itself

A playlist_move command that moves an entry onto itself (both arguments
have the same index) should do nothing, but it did something broken. The
underlying reason is that it checks the prev pointer of the entry which
is temporarily removed for moving.
manpage: lua: cosmetic changes to mp.options section
lua: add some filesystem utility functions

We need this only because Lua's stdlib is so scarce. Lua doesn't intend
to include a complete stdlib - they confine themselves to standard C,
both for portability reasons and to keep the code minimal. But standard
C does not provide much either.

It would be possible to use Lua POSIX wrapper libraries, but that would
be a messy (and unobvious) dependency. It's better to implement the
missing functions ourselves, as long as they're small in number.
TOOLS: add a Lua script to autoload playlist entries

This will load other files in the same directory when a single file is
played. It's an often requested feature, but we definitely don't want it
in the core.
DOCS/coding-style: add a hint that new features should be documented