Download the source
Alternatively, you can use git and clone my public repository:
The interesting branch is
How to continue
The source distribution will not only contain the game's source code, but also all in-game content, e.g. levels and graphics.
Read the instructions on building from source.
This file comes with the source distribution, too, it can be found at
Mac users may instead pull the following repository, which is maintained
by Phil. It has several enhancements to ease compilation and general usage;
it uses the native APIs in several places instead of relying on Allegro 4
You can look at Phil's Lix site if you need further info.