module/script: wip: new plugin, reads data from a user provided script/binary

This module exec’s a script (or binary), specified by the ‘path’
attribute in the configuration.

It then reads tags from the script’s stdout.

The format of the output is:

  tag|type|value
  tag|type|value
  <empty line>

I.e. the script writes N tags followed by an empty  line. This
constitutes a transaction.

When a new transaction is received, its tags replaces *all* previous
tags.

modules/meson.build

@@ -19,6 +19,7 @@ deps = {
   'mpd': [[], [mpd]],
   'network': [[], []],
   'removables': [[], [dynlist, udev]],
+  'script': [[], []],
   'sway_xkb': [['i3-common.c', 'i3-common.h'], [dynlist, json]],
 }