Wonder of wonders

* Created WondrousItemContents attributes table to contain contents of
various wondrous items
* Have wondrous item generator fill in contents (partially or fully) for
items that have contents)
* Add charge limits (not used as charges, though) to determine how
partial an item's contents will be
* Added some missing wondrous items to the wondrous items attributes
table
* Refactored attribute and percentile tests, so that if a table cannot
be found, the error is more explicit than just that the test fixture
setup failed
* Don't mark content items as charged (they don't have charged, just a
count of contents).