Add model comparison plot, deprecation warning Project

[dbrakenhoff]

• Added deprecation warning for pastas.Project

• Added ml.plots.compare() for comparing models on the same figure. The figure is based on ml.plots.results(). See example below.

• Added a test for this method to test_plot.py

[dbrakenhoff]

The failure is being caused by c82df93 which only affects python 3.5 apparently.

[raoulcollenteur]

Just a thought. We could also make this method separate, e.g.,

ps.plots.comparison(ml1, ml2)

I don't have a real preference, you?

[dbrakenhoff]

I'd be fine with it being a separate method. I did it this way because this is how the rest of the plot methods are accessed and thought it might be less easy to find if it was a separate method. Then again, I like the call signature better with ps.plots.compare([ml1, ml2, ...]), so I've changed it.

The warn method allows it to be of type DeprecationWarning, but I'll change it to the logger.warning.

Failure in travis is showing the following message:
TypeError: stem() got an unexpected keyword argument 'use_line_collection'
Odd, but let's see if it works now though.

[raoulcollenteur]

We'll deal with that matplotlib error in the dev-branch. Merging and Closing this PR.