Two issues:
* The notebook cell that actually runs model_train_eval was running it in a
subprocess so while it inherited environment variables from the running
python kernel, it couldn't inherit the tensorflow environment from it.
This resulted in the `set_memory_growth(g, True)` and
`mixed_precision.set_global_policy("mixed_float16")` calls in the previous
cell to be lost.
* TFlite doesn't support "mixed_float16" anyway and causes the model export to
fail spectacularly so it's kind of a good thing it wasn't being applied.
So..
* The tensorflow environment variable and memory_growth setting code was moved
from the notebook cell that also wrote the config yaml to the next cell
which does the train and test. This leaves the "config" cell to just write
the yaml. This is really just a cosmetic change to group functionality
better.
* The code that tried to set "mixed_float16" has been removed but since setting
memory_growth to true is a good thing, the model_train_eval is now run using
runpy instead in a subprocess. This way it's run in the same python kernel
instance and tensorflow environment as the rest of the notebook and inherits
the memory_growth setting.
Resolves: #14
