Thingy things

* Move special material generator to decorators for both magical and
mundane item generators
* Rounded out unit tests for magical weapon generator (still failing)
* Had special material generator handle not letting item get multiple
materials, and double weapon logic
* Refactor ammunition generator to use percentile roll for quantity,
like charges
* Refactor testing for charges and ammunition quantity to be explicit
via test cases
* Clean up some more lingering generators that have been moved to
decorators
* Added tests that slaying arrows get designated foes in specific gear
generator