py: Add hex builtin function.

A one-liner, added especially for @pfalcon :)
diff --git a/py/makeqstrdata.py b/py/makeqstrdata.py
index eaff11b..f8605ae 100644
--- a/py/makeqstrdata.py
+++ b/py/makeqstrdata.py
@@ -16,6 +16,7 @@
 codepoint2name[ord('.')] = 'dot'
 codepoint2name[ord(':')] = 'colon'
 codepoint2name[ord('/')] = 'slash'
+codepoint2name[ord('%')] = 'percent'
 
 # this must match the equivalent function in qstr.c
 def compute_hash(qstr):