Replace hard-coded type strings with constant Enums for memoryjs

[ewpratten]

This PR makes no functional change, but replaces hard-coded strings with enums when specifying a data type to be read through the memory.js library.

Example: 'pointer' -> DataType.POINTER

This both keeps the code (in my opinion) more reader-friendly, and more closely matches the intended usage of memory.js.

The DataType enum is defined in memoryjs.d.ts, and is a typed copy of the constants defined here.

I also switched all references to the ptr datatype to pointer, since they are functionally the same

[ryantheleach]

LGTM, good improvement for future maintenance.

For what it's worth, the definition file ALREADY had restraints on what 'magic strings' would be accepted by readMemory, so on the surface it's a small readability change (with possible side effects I havn't tested) Yes using enums would be more familiar to people who don't use TypeScript on the regular, but I'm not 100% sure on the mechanics of defining an enum inside the definition file, as noted in my review.

Also be aware that Memory.JS already exports a series of constants, they are just unfortunately not grouped nicely into a datatype.

https://github.com/Rob--/memoryjs/blob/master/index.js#L6

So if you really wanted to use hard-coded constants instead of raw strings, even though the type definitions had those strings already in the type, I'd suggest using MemoryJS.PTR etc, and leaving the type definition as-is.