Removed 'bad argument' warnings from config module.

Since Lua handles now all other arguments, there is no need for the
config module to warn if it doesn't recognizes an argument.
Enhanced C string handling.

String length constants include the terminating zero byte and thus end
in `_SIZE` now.  Makes things a bit clearer.

Closes #51
Removed unneccesary prefixes of VFS paths.

It's not needed as PhysFS has no concept of a working directory.
Plus editors can work with the regular paths more easliy.

Closes #54