Changed `iso_Sprite.GfxSprite' to a value.

It was a pointer before, which didn't make much sense since it is
very unlikely that one `grafix_Sprite' would be referred to by more
than one `iso_Sprite'.
Changed how includes work for the `asset' module.

Basically, we were ending up with circular dependencies, since
asset loaders being invoked by the asset db _need_ access to the db
themselves. This may require refactoring for prettiness later, but
for now just including the data headers directly does the trick.
Added a new error for bad texture ids.
Added the `iso_TileSet' type.

Also a loader for files that describe tilesets.
Added GPL and some error checking to `asset/db.c'
Added resources for testing, changed `main()'.

Not a very thorough test, basically just verifying there are no
segfault and poking around w/ GDB to verify the data structures are
as I expect them to be.
Added tileset support to the asset db.
Created a `res/' directory for resources.

They were cluttering up the root directory.
Fixed bug w/ uninitialized pointers.

Oh man, this was a bad one... Heap corruption ftw!
Fixed a few mathematical errors.

This commit is the first of many to come. We now have all the
pieces in place to begin testing the drawing code, so bugs will
start surfacing everywhere.
Added code to bind texture when drawing sprites.

The code just happened to be working because we were only using one
texture (which had been bound when it was loaded).
Added code to turn `map_t' into a proper drawable.
Fixed a major bug in `gen_Heap'.

Forgot to recurse in `heapifyDown()'...
Fixed bug in the tileset loader.

Was interpreting some fields wrong. This is understandable since
the tileset file format is practically obfuscated ... might need
to come up with a better one for the future.
Added some more resources to the manifest.
Added the ability to load a binary map format.

Of course, there are no map files to load right now...
Now everything builds and we have a test render.

Woo hoo! We're just about there (though we desperately need better
tiles).