patches, album artist, etc.

Hello,

Thank you for Emms and all the work you do.  It is a nicely architected
application.
I would not have been able to do all of this without the nice design of
emms.

As promised. here are my changes to Emms.

It took some time to merge my function overrides into the source tree.  I
had given up on contributing as I couldn't see that might be possible.

I ended up with a few random commits to finish it off.
Somewhere in the middle I had defvar problems because I couldn't see the
doc string in the wrong place. Then some scoping issues, it's always the
tiny stupid things.

Ive added more than I thought, these changes bring emms to the point that
it is usable for me.
I did my best to not disturb the defaults or behaviors.

Album Artist iformat is %o for orchestra, instead of %A because album took
A.  That is the worst thing,
There are a few minor inconsistencies in that area, between album and album
artist references.

My use case is as a tango teacher and DJ among the more normal uses.
Album artist and artist are very important for tango and classical music as
it
is usually the orchestra name.

Locking the queue down is very important, it can't be changing as you
browse other playlists
while DJing.

Turning next-mapping into data was an obvious improvement. The default
mapping didn't work at all for my use case.  Def advice is a complicated
way to manipulate that. Genre is really important also. Tango is really
several genres.  Tango, vals and milonga are the short list.
I made an additional map for my tree render and another to match another
TDJ friend's browsing style.  Trying to recruit another user.

There are still problems but they are getting harder to analyze, find and
fix.
Metadata is a real problem.  I haven't seen any info- method work with flac
files yet.
It baffles me that metaflac fails to work in emms when it works great on
the cli.
I had thought native would work too, it's not obvious in the code why they
dont.
info-mpd works the best so far in my experience, and not that well, but at
least it gives album artist with my fix.

My plan is to dig into the info system and tagging next to see why it's not
working.
Also as to why playlists lose their formats. Those are the two obvious
areas that I'm still
unhappy with.

Most of the commits are fairly standalone with the random stupidity fix
here and there.
I'm sure I missed something or violated some conventions, but I hope it's
not bad.
I tried to be consistent and conservative in my naming and choices.

It was borked for a bit in the middle of the commits today, mostly the tree
mapping defvars I think.
It is also browseable on my github. https://github.com/ericalinag/emms.git

Here's the list of changes.

   1. Fix emms-browser-mode so that major-mode is set in time for
   evil-set-initial-state.
   2. Add album artist as an info/node choice
   3. Add album artist to info-mpv and info-metaflac
   4. Add album artist as a format variable, %o for orchestra.
   5. Add Album artist to browse-by, search-by, sort, limit, wiki, etc.
   6. Make tree-next-mapping data driven.
   7. Add ability to lock the active playlist queue to its playlist
   8. Ability to browse a playlist from the meta playlist without making it
   currently active
   9. Ability to send a track from a playlist to the end of the active
   playlist.
   10. Add two more tree maps as choices for tree node mapping.

I hope that you like my work.

Thank you,

Erica