Swapping ASCII font generator for bitmap-based

Makes the "Generate ASCII tiles" function request a bitmap file to work
with, and populate the tileset with bitmap ASCII from that bitmap
instead of font-generated ASCII.
Also fixes the Main() path in build.ant and provides a build.xml so that
Ant can be just started from the directory.

TODO: Check that the tilepage matches the selected tileset dimensions
TODO: Revert to font-based ASCII generation if no tilepage is selected
Font-ASCII generation fallback and fixes

Made the program ask if the user wants to generate old font-based ASCII
if he cancels out of tilepage selection.
Made the program tell the user the required dimensions of the tilepage
if the selected tilepage file is unsuitable.

Should be ready for public consumption now.
Partial-color ASCII tile fix

Bit of old attempt's code managed to remain, making only grayscale
pixels register in tilepages. Fixed now - alpha determines if it gets
copied, grayscale is colored, non-grayscale properly remains unchanged.
Walls, cars, and more

Fixed the appearance of walls, car bodies, and default "overlay"
characters like the item highlight cursor when generated from bitmaps.

Minor tone-down of acid yellow color.
Merge pull request #1 from SeanMirrsen/Custom-ASCII-generator

Custom ascii generator (sigh)