Switch from Vundle to Pathogen

Pathogen is about 1/3 as many lines of code, not to mention that this
commit is itself net negative, but on top of that, it works better too.
With the old Vundle setup, it could bootstrap itself on a fresh install,
but it wouldn't notice any new plugins. With my new Fetch function and
Pathogen, I can install any missing plugins at startup on a per-plugin
basis. Makes it easier to start using new plugins on one machine and
then push the config to my other machine, it auto-fetches the new plugin
on next vim launch.