Various improvements.
Notably, the program now checks the $_GET array to see if it contains a
variable before attempting to grab it.
In addition, updated the documentation on the getBackground method.
Changed the way that files are stored to support teams.
Also updated the code for verifying if an image is valid to reflect the
change in the file naming scheme.
There were a few other improvements scattered throughout the code.
Fixed problems with team banner generation.
Fixed several bugs which were keeping team banner generation from
working.
Unfortunately, it the foldbanner program itself appears to be incapable
of generating team images, making it impossible to verify that the
program is working.
Fixed a bug with caching images.
Fixed a bug where images were always regenerated, even if a cached
version existed.
Cleaned up the code a bit
Changed the getPreviousImage function to fix a logic bug.
Also added a line to ensure that the output folder actually exists
before writing to it.
Added a version variable.
Added a constant "Version" to the program, to keep track of the program
iterations.
Various other improvements as well.
Added documentation for isPreviousImageValid