Add default replace for - to _

Also updated changelog and docs.

Resolves: #549

beets/config_default.yaml

@@ -39,6 +39,7 @@ replace:
     '\.$': _
     '\s+$': ''
     '^\s+': ''
+    '^-': _
 path_sep_replace: _
 asciify_paths: false
 art_filename: cover

docs/changelog.rst

@@ -52,6 +52,7 @@ New features:
 
 Fixes:
 
+* :doc:`/beets/config_default`: Added default replace for - to _. :bug:`549`
 * :doc:`/plugins/absubmit`: Do not filter for supported formats. :bug:`2471`
 * :doc:`/plugins/mpdupdate`: Fix Python 3 compatibility. :bug:`2381`
 * :doc:`/plugins/replaygain`: Fix Python 3 compatibility in the ``bs1770gain``

docs/reference/config.rst

@@ -131,6 +131,7 @@ unexpected behavior on all popular platforms::
         '\.$': _
         '\s+$': ''
         '^\s+': ''
+        '^-': _
 
 These substitutions remove forward and back slashes, leading dots, and
 control characters—all of which is a good idea on any OS. The fourth line