Add a callback to the tornado event loop to signal
successful launch. Not a tornado expert, so the callback
will hopefully only be called once.

Fix #196

Remove annoying trailing whitespaces

Autoformatting editors create unessesary large patches when
changing files with lots of trailing whitespaces

# Conflicts:
#	donkeycar/parts/datastore.py

Fixing math on the tub merge

Add AWS SageMaker instructions

Fix an error when using the donkey tubplot command

Documentation update to include new standard cars

# Conflicts:
#	donkeycar/parts/datastore.py

Remove TensorFlow dependency

Small Documentation changes... 

Assume a compatible flavor of the tensorflow library is
pre-installed. This allows Donkey to be installed on systems
where tensorflow-gpu is installed w.o. having to fiddle with
dependencies.

Since all install instructions in Donkey docs pre-installs
tensorflow already, this is a minor change.

Add instructions to expand filesystem for the Pi

Update the disk image to use tensorflow 1.7 and support pi3b+

# Conflicts:
#	donkeycar/parts/datastore.py