Consolidate repeated macro definitions into one header

The MIN, MAX, CLAMP, MINIMUM, and MAXIMUM macros appear
throughout the codebase with many re-definitions.  Make
a single copy of each in a common header file, and use
the BSD variants of MINIMUM/MAXIMUM due to conflicts in
the system <sys/param.h> headers.

Macros.h

@@ -0,0 +1,16 @@
+#ifndef HEADER_Macros
+#define HEADER_Macros
+
+#ifndef MINIMUM
+#define MINIMUM(a, b)		((a) < (b) ? (a) : (b))
+#endif
+
+#ifndef MAXIMUM
+#define MAXIMUM(a, b)		((a) > (b) ? (a) : (b))
+#endif
+
+#ifndef CLAMP
+#define CLAMP(x, low, high)	(((x) > (high)) ? (high) : MAXIMUM(x, low))
+#endif
+
+#endif