nolearn.lasagne: Create usage and caveats docs

[dnouri]

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The intention here is to write some usage documentation for nolearn.lasagne, and also mention a few of the caveats that have led to user confusion and tickets before.

Let's collect a list of issues that require a note in the docs here:

• [ ] #7: train_test_split does not work for Pandas Series with non Dense Index
• [ ] #13: Ability to Shuffle Data Before Each Epoch
• [ ] #26: Option to make the nets more deterministic
• [ ] #214: max_epochs and re-running fit
• [ ] #163: Example of Loading Pretrained Model
• [ ] #287: scores_train/valid take different parameters than custom_scores

[anything else?]

[cbonnett]

Given that Lasagne had it's first release recently, maybe it;s time to make a small push for nolearn documentation ? I'de be up for helping out.

[dnouri]

Good call. I'll try and start this effort over the next week or two. Thanks for offering your help.