Update README.

Several different mechanisms are supported for enabling/disabling screensaver.
Updated the README to reflect this properly.
Remove hacks to PYTHONPATH used for testing.

Python can handle paths itself, and there was a bunch of unnecesary code
around. For testing, simply use "export PYTHONPATH=$(pwd)" or something alike.
Avoid screwing up the glade xml file encoding.
Cleaned up package-level and pseudo-global vars.

__init__.py had a bunch of variables and utilitary methods. I've moved these
around, making anything that's not needed outside a module private. I've also
moved all path-handling and icon-handling code into a separate modules.
Rewrote bin/caffeine.

Rewrote it to work with the latest changes and for incresed simplicity.
Fix broken imports.
Update version without messing stuff up.

Update the current version without monkey patching glade files overwriting any
source files, while also keeping it consistently in the GUI, CLI, and package.
Don't duplicate a file during installation.
Shorten and simplify setup code.