Use default background colour.

This closes #233 - patch from Mike Savage.
Fake being more responsive.

Fake being more responsive by updating the screen at the start of the
event-loop, not the end.

This closes #232.
Fix bug #214:
* Support both Lua 5.1 and 5.2 by adding wrappers around a couple of Lua
API functions which have changed between the versions.
Merge pull request #235 from jugglerchris/fix_214

Fix bug #214: