Create simple hello world Leaflet Map renderer

[RandomFractals]

to start integrating leaflet

Use world-cities.restbook and world-cities.geojson data file from #6 and #7 for testing renderer hookup and geo data loading.

[RandomFractals]

need to turn this into a leaflet map ...

[RandomFractals]

see #24 for updated geojson text data display and use htl lib from #25 to create leaflet map UI setup.

Use leaflet map setup from this Observable JS notebook for starters: https://observablehq.com/@randomfractals/chicago-speed-camera-locations

or simpler leaflet map setup without marker clusters: https://observablehq.com/@randomfractals/chicago-red-light-camera-locations

[RandomFractals]

Major world cities with marker clusters: