py: Add hex builtin function.

A one-liner, added especially for @pfalcon :)

py/makeqstrdata.py

@@ -16,6 +16,7 @@ codepoint2name[ord('-')] = 'hyphen';
 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):