It is a little ugly since I couldn't get $(wildcard) to expand *.o files
so it just checks if there are any *.c files and then link in the lib.o
based on that.
Ditch the building of an archive (.a) in favour of linking all objects in a
directory into a lib.o file. This makes it easy to link in subdirectories
and more importantly keeps the build logic in the local subdirectories.
Note: after updating you will have to rm **/*.a if you do not make clean
before updating.
