now generating inner and outer connections points. Inner points used to set tracks of train station. Outer ones used for inter-city connection

changed behavior of fix transition. If only one inbound connection is found to empty cell, let cell be empty and instead fix the incoming line to a dead end in seperate step

removed possibility of more than two connection direction to and from the cities. In this manner we procude nicer and more realistic city infrastructures

added city boarder to as forbidden zone for inner city connection. This strictly seperates inner from outer connections. should help us to get nicer infrastructures.

# Conflicts:
#	examples/simple_example_city_railway_generator.py

docs recreate

See merge request flatland/flatland!208

added possibility to limit number of edges of city with allowed connections
changed number of parallel track
changed number of connection points to be defined per side

#95 markdown instead of rst #80

Closes #95

See merge request flatland/flatland!205

get shortest paths from distance map

See merge request flatland/flatland!202