Merge pull request #14 from blinkkin/develop

Update manual to reflect changes: descend by bump/disarm traps.
Hearing sounds no longer abort multi-turn actions
Flying Polyps have stealth ability
Reduced waiting with [s] from 10 to 5 turns
Body types are now Props instead, started Chthonian monster
Some AI optimizations
Heard monsters shown on map
Reduced range of sounds
Removed "was that supposed to do something?" message when reading scrolls with unknown effect
Re-added missing defender awareness check in melee attacks
Add building instructions to README.