Beta Release Surround Sound (v0.5.1)

Release v0.5.1 (Surround Sound) introduces some major new features, completing enough of the "Immediate" goals and adding enough of the next level features that it's finally time to call it a beta release. There's no audio update -- the code name is just a play on the version number.

Bugfixes:

• Some tower doors still  hinging in bizarre ways
• Intro speech can't be skipped (which is tedious if you're familiar with it)
• Lakes in large landscapes don't reflect across whole surface

New features:

• Export/import of initial game state to allow sharing
• Different game types (finish by emptying postbag, or endless mode)
• Scenic details
• ... plus a little surprise