Handful of improvements
- docs(README): update badges link d3f0d4e
- refactor: use DeepReadonly type to avoid unintentional mutations e678168
- chore: define main field 02d0e68
- ci: use node12 and latest for testing 238d766
- style: update docblocks d6b1d36
- refactor: remove _ prefix from private properties 5a2240f
- chore: remove tslint in favor of eslint 8be5438
- chore: update dependencies f4646cf