website clean up

[junpenglao]

I am checking http://docs.pymc.io/, and there are a few places need to be cleaned up.

• API quickstart is under both getting_started.html and examples.html
• Markdown Header within notebook should be ## and the title being ##, otherwise they appear the same on the right panel (e.g., see Sampler statistics and Multiple samplers)
• redundent notebook http://docs.pymc.io/en/latest/notebooks/bayesian_neural_network_advi.html and http://docs.pymc.io/en/latest/notebooks/bayesian_neural_network_opvi-advi.html

[fonnesbeck]

Let's find a non-generic theme for this too. Should I hire 99designs again?

[ColCarroll]

Here are a bunch that might work. I have not picked out a favorite yet!

https://github.com/yoloseem/awesome-sphinxdoc#themes

[junpenglao]

i actually dont mind the default as it suits well with pymc3 blue;-)

@ColCarroll https://github.com/crate/crate-docs-theme is quite nice

[denadai2]

I'll take care of some fixes :)

PS: I like more the blue one, although it is standard