Continue the Rust implementation

[dabreegster]

• [ ] Improve performance (parallelize, reconsider the conversion to geo, check parsing and writing)
• [x] Come up with a simple way of sanely viewing the output to manually validate. geojson.io and similar aren't good for spotting adjacent line-strings; probably make a custom Leaflet style
• [ ] Optionally split when some property (an OSM ID) changes
• [ ] Ignore direction (optionally?)
• [ ] Split line segments when needed
• [ ] Validate to the R implementation's output, and compare performance

[dabreegster]

For perf, keep an eye on https://github.com/georust/geojson/pull/223

[dabreegster]

Converted into smaller issues