Address the 'long tail of visualization' in the documentation

[jlstevens]

HoloViews makes common operation and visualizations very easy. That said, HoloViews needs to be flexible enough to scale to finely tweaked or highly customized visualizations.

Here are our current recommendations:

• First make sure we haven't already exposed the style or plot options you are looking for.
• If there is some style keyword that needs to be passed to the backend (i.e. matplotlib for now) the allowed keywords can easily be extended as detailed in the FAQ. If you believe it ought to be available for all users, please submit a pull request explaining briefly why it is useful and showing which style_opts should list it, and we'll make it available by default
• The finalize hooks need to be documented as these hooks are the easiest way for a user to change the behavior of our plotting system with minimal code.
• Writing a new Plot class and if necessary a new Element type, typically extending from some existing class. Obviously the most work but extremely worthwhile, as your new plot will then compose nicely with the rest of HoloViews (automatic support for layouts, overlays, animation, the options system and more!).
• Finally you can consider exporting to SVG and tweaking the figure externally e.g. in Inkscape. This is only recommended for very minor changes just before publication as such tweaks are not reproducible!

We should definitely consider authoring a new notebook tutorial on this topic.

[jbednar]

I've updated the above recommendations slightly by editing them.

[jlstevens]

I have now linked to this issue from the FAQ page: 44270ca9