fluidsynth: new decoder plugin for MIDI files

There are a few problems left in this plugin:

- fluidsynth decodes in real time, while MPD prefers to buffer as
  quickly as possible; as a workaround, this plugin uses a timer
  object to synchronize with real-time playback

- I don't know yet how fluidsynth tells me when the song has ended

- the "soundfont" configuration setting is not yet documented, and it
  will likely change soon (in favor of a per-decoder configuration
  block)

INSTALL

@@ -98,6 +98,9 @@ Multi-codec library.
 libsidplay2 - http://sidplay2.sourceforge.net/
 For C64 SID support.
 
+libfluidsynth - http://fluidsynth.resonance.org/
+For MIDI support.
+
 
 Optional Miscellaneous Dependencies
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