Custom dog-action

Merge pull request #57 from skx/48-rug

Bugfix: Examining rug shouldn't always trigger behaviour

Merge pull request #45 from skx/44-clean-exit

Correctly terminate the game cleanly on death/quit

Fixed location of encryption helper

Merge pull request #40 from skx/38-encryption

Generate encrypted versions of the ZX Spectrum game

Merge pull request #36 from skx/33-trapdoor

The trapdoor has three logical states.

Updated ZX Spectrum port to use 64-character output.

This is accomplished via a tiny font, and a new output routine hooked
up to stream #4.

Merge pull request #31 from skx/30-toggle

30 toggle

Restrict input length for ZX Spectrum

* Update the input routine to cap input at a sane size, to avoid
  scrolling on input.
* Reworded "invalid command" message to fit on the spectrum screen.

Merge pull request #28 from skx/27-spectrum

Introduce a ZX Spectrum Port.