Fix indentation, compile tests, gitignore

• Make indentation consistent: Two spaces, no tabs, and definitively no mixture of tabs and spaces on the same line. This will make the code more readable outside of "smart indenting" editors like EMACS.
• Fix the compilation of the tests (by unbreaking the Makefile for them) and compile them by default.
• Add a .gitignore file.

Whenever I've looked at this code in the last years (e.g. when discussing with Jim), it's been obvious that what was readable on my setup back then isn't neccessariy readable on other editors or other editor configurations. Also I realize that I had some very bad habbits for unneccessarily "compactifying" code by dropping "unneccessary" brackets etc., and writing incredibly long lines filled with magic numbers. The main goal of this patch is to make things a little more readable.