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.

CPUMeter.c

@@ -20,13 +20,6 @@ int CPUMeter_attributes[] = {
    CPU_NICE, CPU_NORMAL, CPU_SYSTEM, CPU_IRQ, CPU_SOFTIRQ, CPU_STEAL, CPU_GUEST, CPU_IOWAIT
 };
 
-#ifndef MIN
-#define MIN(a,b) ((a)<(b)?(a):(b))
-#endif
-#ifndef MAX
-#define MAX(a,b) ((a)>(b)?(a):(b))
-#endif
-
 static void CPUMeter_init(Meter* this) {
    int cpu = this->param;
    if (this->pl->cpuCount > 1) {