Pictures now are created individually during the "img" request, and not at script runtime.

The change to creating the pictures at img request time instead of
script request time should speed initial page load time, even if total
time gets a bit longer because of more cgi requests and addtional file
opening.
Also:
- resized images now get written to a separate "cache" folder
- height and width attributes added to img tags
- more things made web-safe when funky characters are involved
- changed the resize logic a bit to maximize picture size inside a
defined rectangle
- stripped out admin function that deletes cache… just rm on the cache
folder if you want to clean it