Lost qualifiers on inverse attributes and uniqueness rules

Closes issue #261.

Fixing these problems required making changes to the parser  itself, as well as changing which structures were used to represent the data.

Different structures necessitated changes to exp2cxx and exppp; exp2python doesn't seem to need any changes.

Adds 4 tests, 2 each for exppp and exp2cxx, to verify that qualifiers are not lost for inverse's or unique's.