Added support for PNG podcast cover art
Fixed error in comment
create tempdir if it does not already exist
This seems like a bug,  I had to change this to get the script to run.

prior to this fork, I was running a modified copy of 1.7.1 for the last 2 years and hacked it up a bit to meet my needs I don't recall
how this ended up in my copy, is missing from upstream, but appears to be necessary for the script to run with
my configs.
my server was throwing an error about  $_SERVER['DOCUMENT_ROOT'] not being an index when running dir2cast from the command line.
I moved it inside the if that only gets run when running as a webserver script.
added support to item specific images.  just create image files in the same name as the mp3 file but with .png or .jpg extensions and they will get incorporated like how the .txt files are.
added support for writing output to a rss.file as an alternative to writing to stdout.
correcting syntax error to commit e070b38
cleaning up some output from added in commit 65618e1
moved MP3_URL definition so it can be defined in the directory specific ini file
and supporting changes
committing inifile for OUTPUT_FILE support introduced in 65618e1
added ini parameter to set the content type on the atom:link element