V2.0 🎉

Updates to react@18, leaflet@1.8 and react-leaflet@4
- Compatibility with react@17 and react-leaflet@3 still likely considering the high-level nature of this wrapper, may need to install with --legacy-peer-deps
Dropping support for react-leaflet@2
Fixes bad typescript typings for layer components (#15)
Add deprecation warning for BasemapLayer (#14)
Completely overhauled example, now available through github pages, with code samples
Dropping pure javascript example in favor of TS example, with JS sample code built in to the example

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