Initial Linux

Everything that works in DOS should work in Linux (except for music, sound, mouse, and joystick support). There are also some improvements (IMP commits) that could be backported to DOS at some point:

• Fixed off-by-one memory corruption bug when creating an empty object or scroll.
• Fixed various range check errors (out of bounds access and integer overflow).
• Fixed stats corruption bug involving when a player is next to an item with stats on a conveyor.
• Fixed potential memory corruption when picking up an objects or scroll and then going to another board.
• Fixed two crash bugs that could be provoked ingame (ZZT Encyclopedia bugs)
• Replaced numeric I/O errors with English explanation
• Corrected KEY_HOME and KEY_END constant values and added support for HOME/END to editor
• Added international key support to level title prompts, etc.