Unit test framework, hover tests, fix hash collision bug

[WillLillis]

This PR does a few things

• Changes the information maps (names_to_instructions, names_to_registers, and names_to_directives) to hold owned copies of their respective data, rather than references to the data inside of separate Vec. This change was made in order to facilitate easier setup for unit tests, as well as in preparation for the refactor to support Use serde for deserializing the data sources #75.
• Add a basic unit testing framework. Essential (read-only) parts of the server (just the aforementioned maps for now) are initialized and placed in a static variable accessible to all of the tests.
• Added unit tests for hover capabilities. The tests added don't offer complete coverage, but do touch a decent chunk of use cases. As bugs are reported (and fixed), the associated reproduction cases can be added as further regression tests.
• Fixed hash collision bug. To my surprise, the order in which instructions were added to the hashmap was different between different runs of the server. This caused certain instructions with associated names that were also valid instruction names (e.g. one of MOV's associated names is MOVQ) to overwrite the original instructions in the names_to_instructions map.
• While debugging I also updated the quick_xml crate that we depend on for parsing our various info files.

Next steps include:

• adding testing for other features (autocomplete, goto defintion, find references, etc.)
• general cleanup for the testing framework (e.g. supporting/ testing different server configurations)