config: Add config for data/config/cache directories

Issue #843

docs/config.rst

@@ -68,6 +68,18 @@ Core configuration
     The original MPD server only supports 10000 tracks in the tracklist. Some
     MPD clients will crash if this limit is exceeded.
 
+.. confval:: core/cache_dir
+
+    Path to directory for storing cached information.
+
+.. confval:: core/config_dir
+
+    Path to directory with configuration files.
+
+.. confval:: core/data_dir
+
+    Path to directory with data files.
+
 
 Audio configuration
 -------------------

mopidy/config/__init__.py

@@ -18,6 +18,9 @@ logger = logging.getLogger(__name__)
 _core_schema = ConfigSchema('core')
 # MPD supports at most 10k tracks, some clients segfault when this is exceeded.
 _core_schema['max_tracklist_length'] = Integer(minimum=1, maximum=10000)
+_core_schema['cache_dir'] = Path()
+_core_schema['config_dir'] = Path()
+_core_schema['data_dir'] = Path()
 
 _logging_schema = ConfigSchema('logging')
 _logging_schema['color'] = Boolean()

mopidy/config/default.conf

@@ -1,5 +1,8 @@
 [core]
 max_tracklist_length = 10000
+cache_dir = $XDG_CACHE_DIR/mopidy
+config_dir = $XDG_CONFIG_DIR/mopidy
+data_dir = $XDG_DATA_DIR/mopidy
 
 [logging]
 color = true