Proposed new encoding: bz2tile

[Matt Campbell]

Having realized that the encoding I proposed yesterday was quite naive, 
I now propose a new encoding based on bzip2 compression, tentatively 
called bz2tile.

The uncompressed representation starts with the tile size:

	U16 tileSize;

As with Hextile and ZRLE, if the dimensions of the rectangle aren't 
exact multiples of the tile size, the last row and/or column of tiles 
are smaller.

Each tile starts with a subencoding field:

	U8 subencoding;

There are three subencodings:

0 - Raw:

The subencoding field is followed by the raw pixel data for the tile:

	CPIXEL data[tileSize * tileSize];

1 - Solid:

The subencoding field is followed by the solid color of this tile:

	CPIXEL solidColor;

2 - Palette:

The subencoding field is followed by the maximum palette index:

	U8 maxIndex;

Since palette indices are zero-based, this is the size of the palette 
minus one.  This subencoding therefore allows a palette of up to 256 
colors.  This subencoding never packs multiple pixels into a single 
byte; bit-packing is the job of the Huffman coder used by bzip2.

The maxIndex field is followed by the palette:

	CPIXEL palette[maxIndex + 1];

The palette is followed by the indices for this tile:

	U8 indices[tileSize * tileSize];

Any questions or concerns regarding this new encoding?  I'm about to 
implement it.

Matt