Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/beetsplug/loadext.py

@@ -0,0 +1,44 @@
+# This file is part of beets.
+# Copyright 2019, Jack Wilsdon <jack.wilsdon@gmail.com>
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+"""Load SQLite extensions.
+"""
+
+
+from beets.dbcore import Database
+from beets.plugins import BeetsPlugin
+import sqlite3
+
+
+class LoadExtPlugin(BeetsPlugin):
+    def __init__(self):
+        super().__init__()
+
+        if not Database.supports_extensions:
+            self._log.warn('loadext is enabled but the current SQLite '
+                           'installation does not support extensions')
+            return
+
+        self.register_listener('library_opened', self.library_opened)
+
+    def library_opened(self, lib):
+        for v in self.config:
+            ext = v.as_filename()
+
+            self._log.debug('loading extension {}', ext)
+
+            try:
+                lib.load_extension(ext)
+            except sqlite3.OperationalError as e:
+                self._log.error('failed to load extension {}: {}', ext, e)