cleaned up common.h, added initial ideas for signal handling code and
added a couple of sort functions to array.c

I just reorginized common.h and got rid of some unused code I had lying
around.

For error handling I'm not 100% sure how I'm going to do it, but I added
code to use a seperate signal stack in c and I'll probably use the
sigusr signals as a base.

I added insertion sort(useful for small arrays) and slow sort(because
it's hilarious)
Merge branch 'master' of github.com:hitchiker42/SciLisp