* Make some LCD display related things globally accessible
* Deprecate `read_data` to avoid confusion (use `send_cmnd` instead)
* Allow arbitrary data for `send_msg` and `get_msg` (with optional parameter)
Red Mud -> Lye/Desert Cobble
The filter is an entirely passive machine.
Additional changes:
* Remove `not_in_creative_inventory` from battery (forgotten in #29)
* Improve pump leftover handling (needed for the filter)
* markdown2formspec.py: Switch to Python 3 (Python 2 is deprecated)
