MobIndexData changes

[mattgodbolt]

• Made a few things ClassCase vs SHOUTY_OLD_STYLE
• Extracted a "Dice" class. Wrote tests.
• Extracted a few macros, get_hitroll and get_damroll
• Made test output a bit nicer (CatchFormatters.hpp)

[mattgodbolt]

Just here for show & tell. Will merge tomorrow if all still looks good (tested a bit locally, will test more).

[mattgodbolt]

Testing looks good: will fix up build errors.