[#179] Add build script, eslint, rollup

[krbz999]

Closes #179.

• Added eslint.
• Performed linting.
• Added rollup.
• Updated build script to bundle the module.
• Fixed any circular dependencies.

To install dependencies locally, run this command:

npm ci

To run the build script locally for testing, run this command:

npm run build

and then edit the module.json to point esmodules to module.mjs. (Don't commit that change, it is for testing only.)