Replace lodash dependencies with native code

[andrew-pyle]

I would like to use this library on the front-end for parsing USA State abreviations & names, but the 5.5kB (minified & gzipped) size is too large to justify the inclusion.

This PR removes all 3rd party dependencies and replaces them with Javascript built-in functions. ~92% of the npm package's size was from lodash dependencies.

Analysis from https://bundlephobia.com/package/[email protected].

All tests passed locally, so I do not believe I've made any inappropriate assumptions about the library's data types.