mem: Change used_mem semantics, so that it matches vm.percent and htop's memory usage report

i3pystatus/mem.py

@@ -24,9 +24,11 @@ class Mem(IntervalModule):
 
     def run(self):
         vm = virtual_memory()
+        # This follows the same algorithm used for vm-percent
+        used = vm.used - vm.cached
         self.output = {
             "full_text": self.format.format(
-                used_mem=int(round(vm.used / MEGABYTE, 0)),
+                used_mem=int(round(used / MEGABYTE, 0)),
                 avail_mem=int(round(vm.available / MEGABYTE, 0)),
                 total_mem=int(round(vm.total / MEGABYTE, 0)),
                 percent_used_mem=vm.percent)