misc tweaks/fixes

* don't start player behind house
* add initial random zombies around the board
* fix reload loophole
* reload upon start of game
* more options for toggling weapons (pgup/pgdown/enter)
more tweaks

* click or space to restart
* click to unpause
* "P" to pause
* font tweaks
* zomg message at start of game
restore background, fence tweaks
zombie sounds
render bullet trajectory lower
moar sprites, fix respawn bug