extensions.py: use argparse for arguments

We're going to make more use of this later

src/extensions.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+import argparse
 import sys
 from xml.etree.cElementTree import parse
 
@@ -111,14 +112,18 @@ def emit_module(module, output):
 
 def main():
     # Parse the xml file
-    output_file = sys.argv[1]
+    parser = argparse.ArgumentParser()
+    parser.add_argument('output')
+    parser.add_argument('inputs', nargs='+')
+    args = parser.parse_args()
+
     modules = []
-    for input_file in sys.argv[2:]:
+    for input_file in args.inputs:
         parseFile(input_file, modules)
 
     assert xproto != None
 
-    with open(output_file, "w") as output:
+    with open(args.output, "w") as output:
         output.write("/* Auto-generated file, do not edit */\n")
         output.write('#include "errors.h"\n')
         output.write("#include <string.h>\n")