metadata: add libavcodec > 54 compatibility

libavcodec55 brings some API changes, including CodecID => AVCodecID.
Add a compatibility wrapper so we can build with libavcodec >= 55.
portability: add support for Illumos

This still won't work on older Solaris systems, but modern Illumos
at least should build and run now.
metadata: more libav10 compatibility changes

Add a couple more compatibility wrappers.
metadata: get embedded cover art from video files using libavformat

Newer version of libavformat can grab cover art, so we'll go ahead
and use it.  We also need to make sure we don't confuse cover art
with a normal video stream.
metadata: get rid of some unnecessary mallocs
Update ignores file and remove obsolete include from metadata.h
Rename album_art_name_s to linked_names_s

Give the struct a more generic name so it can be re-used in other places
Add setting to change metadata file name

New config option 'metadata_names' which can be a list of /-separated
files that get checked for metadata before the fallback <filename>.nfo
is checked. By default this metadata file is 'movie.nfo'
Add option to add list of (comma-separated) entries to DB

Refactor code to be able to read values from lists in the nfo metadata.
This enables us to add multiple actors/genres to media and serve them as
a part of metadata for clients. The XML library (minixml) is not ideal and
traverses the xml file backwards... *sigh*
Add new metadata info (year, actors, director)

minidlna already has support for these items, yet they
are never read from the NFO file. Use year if it exists
(instead of timestamp) and add actors & director
Support for short&long-descriptions

Add support for sending 'tagline' and proper long description
in the UPNP reply. Needs DB upgrade as there is new column
Send more-appropiate reply for director and album-art

If mime-type is video, send director as upnp:director as
this is more understood by clients.
Also always send albumArtURI as this is read by some clients to show
icon of media file
DB upgrade is not performed if DB_VERSION is updated
Extract MPAA rating from metadata.c

Add support to extract mpaa rating from the file metadata. Present this as upnp:rating to clients
Add author to metadata

Add writer information to metadata and present it as upnp:author
Send director/creator in response to a single filter, we are running out...
Remove dynamic nfo name.

Since we only support XBMC format, it is either <filename.nfo> or movie.nfo
[refactor] Add a define for ALL_FLAGS
Fix an issue where to much memory was allocated. Second parameter to calloc is element size
Merge branch 'nfo_metadata' of github.com:Darkvater/minidlna into nfo_metadata

Conflicts:
	metadata.c
	metadata.h
	minidlna.c
	options.c
	upnpglobalvars.c
	upnpglobalvars.h
	upnpsoap.c
	utils.c
	utils.h