small refactor and cleanup

stdlib/mem.sl

@@ -0,0 +1,15 @@
+import stdlib.sl
+
+: alloc
+    0      # addr hint (NULL)
+    swap   # size
+    3      # prot (PROT_READ | PROT_WRITE)
+    34     # flags (MAP_PRIVATE | MAP_ANON)
+    -1     # fd
+    0      # offset
+    mmap
+;
+
+: free
+    munmap drop
+;