Changed the resource directory!

It is still hardcoded, but this commit changes it from
"/home/luke/.ultimate_pong" to "/home/luke/.PpM".
Added some resources to the source tree.

So far, only an icon and the default config file have been added!
Fixed a typo in src/common.h.

The "surface" in pong::runtime_assert_surface was misspelled as
"surfaec". I fixed that, luckily nothing actually called it!
Added window parameters to SDL initialization.

That means loading the icon and setting the caption text.
Updated the menu to read "Pong Plus More".

This is a welcome replacement to the old "Ultimate Pong" title already
there.