Changed the playing code to use Playlists managed by a PlaylistManager. This allows you to have randomized playlists and stuff. Also, you can now access special functions via the contents of RFID tags. See the README for a list of available modes.

README.md

@@ -22,3 +22,29 @@
 | BTN_VOL_DOWN | | 32 |
 
 Buttons pull to GND if pushed -> Internal Pull-Up needed!
+
+# RFID stuff
+The mapping of rfid tags to files uses the ID of the
+tag. Create a file `ids.txt` in a folder containing
+one or more IDs will lead to the folder beginning to play
+when a tag with that id is on the reader.
+
+The ID should be a 8 character long, downcase string
+containing the ID in hexadecimal. E.g. `23b1aa7d`.
+
+## Special modes
+You can also save data on the tags to further manipulate
+the system. Position of the data is irrelevant, the whole
+tag will be searched.
+
+Using `[random]` will play the files in a random order.
+`[random:2]` will randomize everything except the first 2
+files. This can be useful for having the favorite song of
+your kids playing, but after that getting a bit of randomness.
+
+Using `[lock]` will turn this key into a key for the locking
+mode. Scanning the tag enables locking mode. The next album
+started will keep running until the end. Removing the tag
+will be deactivated, as are the buttons for prev and next
+track. You can disable locking mode by again scanning the
+lock tag again.