Add --optimize-img={1,2} -- performs postprocessing on images

This adds basic post-processing to images. At the moment, it only
performs actions for the png output type, but changes to work for
jpeg will be exceptionall minimal.

optimizeimages.py

@@ -0,0 +1,21 @@
+import os
+import subprocess
+import shlex
+
+def optimize_image(imgpath, imgformat, optimizeimg):
+    if imgformat == 'png':
+	if optimizeimg == "1" or optimizeimg == "2":
+            # we can't do an atomic replace here because windows is terrible
+            # so instead, we make temp files, delete the old ones, and rename
+            # the temp files. go windows!
+	    subprocess.Popen(shlex.split("pngcrush " + imgpath + " " + imgpath + ".tmp"),
+		stderr=subprocess.STDOUT, stdout=subprocess.PIPE).communicate()[0]
+	    os.remove(imgpath)
+            os.rename(imgpath+".tmp", imgpath)
+
+	if optimizeimg == "2":
+	    subprocess.Popen(shlex.split("optipng " + imgpath), stderr=subprocess.STDOUT,
+	        stdout=subprocess.PIPE).communicate()[0]
+	    subprocess.Popen(shlex.split("advdef -z4 " + imgpath), stderr=subprocess.STDOUT,
+	    	stdout=subprocess.PIPE).communicate()[0]
+