Remove unused "context" argument to "generate_catcher"
Merge pull request #50 from Chris00/ctx

Remove unused "context" argument to "generate_catcher"
"generate_catcher" passes "pos" to the "maker"

This streamlines the uses of "generate_catcher" because it was often
wrapped to extract the position of its last XML argument.  Also remove
the "pos" argument to "attr_producer" (never used).