Trainplot

New:
* refactoring
* experimental plotly support

New:
* Added a `plot` function, that can be used without prior initialization to plot something in the current cell without further custumizations
* `tp.close()` doesn't have to be called anymore, because all updated plots will automatically be "closed"/updated when a cell execution finishes
* updated README and examples

New:
* tf/keras callback
* more customization options with `axis_custumization` argument
* optional threading with `threaded` argument
* base class, which receives plot init and update functions. Should also work for non-matplotlib plotting. (`from trainplot.trainplot import TrainPlotBase`)
* more documentation / code comments
* example notebooks

basic functionality is now implemented and documented