tilecache-2.99

• added an include config option that loads diferent modules
• added config modules for file, url, postgres db, and memcache
• added doxygen comments to some code and a doxyfile
• restrict height and width of wms requests to max of 4096 x 4096
• add layer config item expired to "expire" tiles based on a timestamp test the mtime of each tile against the layer config expired setting and rebuild if nessasary Disk cache ONLY!
• fix cache misses caused by casts to int in getcell(), should be round()