switched back to load_resource in rail_env test. passed load_from_package arg down to from_file generators.  switch default renderer to PGL from BROWSER. Added conditional import for flask_util in rendertools to hopefully avoid some startup delays and hanging tests.  Added os.makedirs to intro_flatland 2.1 for saved frames folder.  Removed explicit gl=PILSVG

This resolves issue #273

updated examples

This resolves issue #273

At each step we first check for possible malfunctions.
THen we apply them and do all the agent steps
At the end we look at what agents should be fixed. This lead so to:

Current malfunction value says how many step calls are necessary till agent can move again

e.g. malfunction = 2, we have to call step() twice untill the agent can move again.

Code cleanup

It now gives the probability that an agent breaks at given time step
given the number of agents and the rate of failures of a single agent.
These number now need to be much larger.... otherwise we will have alot of failures

Updated example

Adresses issue #263

Adresses issue #263

Fixes the examples

Fixed how we handle agents off the grid with the observation example

calculating max possible number of cities and aborting if only one city can be built. Also updated the way we chose city orientation.

add named tuple for result of schedule generator and add max_episode_steps to the schedule generator