Another bunch of cool updates here, mostly related to region 4 (mountain/evil castle)

Traps/interactive objects:
- added a fireball-firing statue, with user-definable shoot rate and shoot speed
- added circular saw trap that moves between user-defined flags at a user-defined speed
- added disappearing tiles
- added portals which teleport characters and objects from one to another (based on user-defined Portal ID)
- added swinging pendulum axe traps, with user-definable movement speed and swing angle

Music:
- another new music track, "The Illusionist"

World objects, added for region 4:
- added snow! which looks really cool - turned on/off in cutscenes
- added bats that flap around and cling to surfaces
- added lava
- added mountain-top background tiles
- added 'evil skull' doorway block
- added various evil castle and mountain decorations: candlesticks, prison bars (foreground), barren trees and bushes, background mountains, green torch, snowman, health pool (decorative only), skeletons, guillotine (decorative), broken barrel, broken vase, pumpkins, giant sword, tombstones, evil pentagram, new spiderwebs, gargoyle statue, new background mountain foliage

Optimisations and tweaks:
- worked out a substantial physics code optimisation which will improve game play on weaker computers
- changed the goblin so that he doesn't switch to 'pushing' mode with small objects
- changed cannonballs so that they do not kill when moving slowly
- key rebindings can now be carried out, from the Settings window

Audio:
- added villagers 'thump' noise when they run into walls and knock themselves over
- added a new footsteps sound for the goblin when running on soft surfaces
- added sheep galloping and bleeting sounds
- added cow moo and munching sounds

Map editor:
- hero names and creature names now default to real player names downloaded from our database