Fixes #96

This fixes issues with type declarations for imports in various environments. Checks all the boxes at https://arethetypeswrong.github.io/?p=ignore

Changes

• Added @typescript/eslint to facilitate testing
• Removed the index.mjs build because it shouldn't be needed anymore and didn't always work
• Added cjs and mjs tests for testing different situations
• export = import -- I believe this is the "correct" way to declare the exports for a CommonJS module. Other approaches work in many cases, but this is the only way that works for everything.
• module.exports.isPathValid = isPathValid -- Apparently there's a difference between this and factory.isPathValid = isPathValid and in some situations, named exports only work when set directly on exports.

Compatibility Considerations

In some situations, this requires that people enable esModuleInterop in their tsconfig.json in order to use import ignore from "ignore". Otherwise they need to use import * as ignore from "ignore". I think it's extremely unlikely that people will find themselves in this situation, but it does technically make this a breaking change.