[WIP] Improvement: #20 add option to generate animated examples

[swistakm]

This refers to #20.

This is just a proof of concept. Over time the gen_example module became riddled with kludges. It is a good opportunity to refactor it into more reliable and extensible offscreen renderer.

@supudo what do you think about that?

TODO:

• convert existing examples with :click: option to animated ones (only if it makes sense)
• refactor the code in gen_example.py
• add option to specify fps and duration of the animation
• fix requirements issue in builds on Travis

[swistakm]

Some preview of how it looks like in the documentation:

[supudo]

Hey,

I couldn't manage to setup image generation on my side for whatever reason (I'm on py35).
Can't give very sophisticated opinion on this yet, but for me it would be useful to combine the two builds - module and docs.

Also, this is a bit off-topic from this thread, but lots of the code are mixing py2 and py3, which @Wiatrogon fixed with the amazing _bytes() function :), so this also impacts the docs generation. One idea is to change all function params from char to str and use that function, but i'm not very familiar with py2 to recommend such an approach.

Cheers,
S.