Add POPCOUNT function (#2166)

man/rgbasm.5

@@ -436,6 +436,8 @@ equals $roman clz ( n )$, the count of leading zero bits in the binary represent
 .Ar n .
 .It Fn TZCOUNT n Ta Returns $roman ctz ( n )$, the count of trailing zero bits in the binary representation of
 .Ar n .
+.It Fn POPCOUNT n Ta Returns how many one bits are in the binary representation of
+.Ar n .
 .El
 .EQ
 delim off