Cleaned up the XML parser grammar.
Cleaned up the XML parser grammar.

This resolves all shift/reduce and reduce/reduce conflicts that were previously
present.

dfockler/oga,altmetric/oga,dfockler/oga,ttasanen/oga,altmetric/oga,altmetric/oga,jeffreybaird/oga,ttasanen/oga,YorickPeterse/oga,dfockler/oga,jeffreybaird/oga,jeffreybaird/oga,YorickPeterse/oga,altmetric/oga,dfockler/oga,jeffreybaird/oga,YorickPeterse/oga,ttasanen/oga,ttasanen/oga,jeffreybaird/oga,YorickPeterse/oga,ttasanen/oga,altmetric/oga,dfockler/oga,YorickPeterse/oga