[FEATURE REQUEST] Make graph simple as possible

[LdDl]

Is your feature request related to a problem? Please describe.
There are too many generated edges/vertices after parsing OSM (via edge expansion). Contraction hierarchies algorithm could take very much time to process all set of vertices. I'd suggest to implement Edge contraction to reduce size of graph for further contraction hierarchies algorithm

Describe the solution you'd like and provide pseudocode examples if you can
Find all vertices with degree == 2. Then recursively:

while exists vertex v with degree 2:
    - remove v and the 2 outgoing edges
    - add a new edge between the neighbours of v
    - the weight of the new edge is the sum of the weights of the deleted edg

reference - https://stackoverflow.com/questions/54954644/algorithm-to-simplify-reduce-graph

Additional context

• Would be cool to have an optional flag for CLI (for debugging purposes) also
• Some numbers for "before" and "after" (kinda benchmark) on specific graph

[LdDl]

Some kind of workaround could be found in #12