Add quick sort manual tail-call optimization

Before, sorting `evil.txt` would have a massive 9,000+ stack size.
Now it has a stack size of only 30 or so.

We do this by, rather than making two recursive calls to quick sort,
we only do a recursive call on the smaller half. For the larger half,
we replace the left and right values in the current call and loop.
This way, if a poor choice of pivot is made and, for example, we
partition a block of size N into pieces 1 and N-2, we don't create
a new stack entry for N-2, but instead reuse the current one.

Fixes #62

This also fixes a unary minus on an unsigned integer, which creates
problems for some compilers (notably MSVC).

Makefile

@@ -28,4 +28,4 @@ benchmark: benchmark.c sort.h
 	$(CC) $(CFLAGS) benchmark.c -o benchmark
 
 format:
-	astyle --options=astyle.options sort.h bitonic_sort.h demo.c multidemo.c stresstest.c benchmark.c
+	astyle --options=astyle.options sort.h demo.c multidemo.c stresstest.c benchmark.c