Added private addon count at the bottom of update addon panel - just in case people don't read the FAQ and attempt to update a private addon.
Added a lot more error checking - this should give you a better idea of what gmad/ gmpublish is complaining about.
Added default directory check, this will check to see if Garry's Mod is installed on your C: drive, and if it is, it skips asking you where it's located.
Complete removal of jQuery, which should make future debugging a lot easier, also makes the code a lot easier to read and understand in my opinion.