Allow Topojson dicts to be parsed into Topology

[mattijn]

This PR will fix #124. This PR provides an enhancement by supporting reading topojson files. This enables loading Topojson structured json data into a Topology and process them further. Such as the following example:

import json
import topojson

# load topojson file into dict
with open("tests/files_topojson/nybb_from_mapshaper.topojson", 'r') as f:
    data = json.load(f)

# parse topojson file using `objects_name`
topo = topojson.Topology(data, objects_name="nybb")

# apply toposimplify, serialise into a geodataframe and plot
topo.toposimplify(5000).to_gdf().plot()

Not all functions are working yet (eg to_alt()), but it is a good start.

[mattijn]

Serializing to altair is included as well as more tests. Made sure all other tests are still passing