* Reduced PROGMEM / DRAM usage slightly (Using defaults w/HW5: Before -> 214,668 bytes / 5,757 bytes; After -> 213,414 bytes / 5,751 bytes)
* Optimized some menu options and calls
* Added more string constants and implemented them where found.
* Fixed some stylization
* Constants should always be uppercase.
* Features should use the `ENABLE_<feature name>` format.
* Options for features should use the `OPTION_<feature name>_<option name>` format.
* Added ENUMs for more clarity and better type checking.
* Moved some defines over to `constexpr` and `const` types. These are preferred over preprocessor constants when not intended for use with `#if` and other preprocessor language.
The `setVoltage()` function should be called even when `ENABLE_VSELECT` is disabled because `ENABLE_3V3FIX` also uses it. There is no resource cost to do this as when both options are disabled the compiler will optimize this function out. This just "future proofs" the code so if that function ever does more it doesn't need updated everywhere. This applies to `setup_FlashVoltage()` as well.
The changes to OSCR.cpp are just for code formatting and additional comments to clarify this.
