#2899: (draft) add Weibull AFT and censoring examples

[jazzmuesli]

This is an early draft of

• Enhancement of Survival Analysis documentation #2899 copied code from https://github.com/pymc-devs/pymc3/pull/1870/files
• https://github.com/junpenglao/Planet_Sakaar_Data_Science/blob/master/PyMC3QnA/discourse_1107.ipynb

I think it's too early to merge and more work needs to be done.

[junpenglao]

I think it is appropriate to put these notebooks under a new session and index them on the website:

• Analysis of censored data
  • censoring analysis (fix Enhancement of Survival Analysis documentation #2899)
  • Bayesian Survival analysis (the note currently in the doc but not indexed: http://docs.pymc.io/notebooks/survival_analysis.html)
  • Basic Weibull model (the new notebook here)
  • Bayesian Survival analysis with weibull AFT (http://austinrochford.com/posts/2017-10-02-bayes-param-survival.html)

[fonnesbeck]

These are looking good. Make sure they are annotated with markdown cells throughout the notebook. Many of the comments can be moved out of code cells and into their own markdown cells. A bit of interpretive text at the end would be helpful too.

[AustinRochford]

Agree with Chris that breaking some of the larger code cells apart and adding explanatory text would be good.

[springcoil]

Any update on this @jazzmuesli?
It looks awesome in fact, with a bit of polish - this would make a great contribution to the docs - I agree with the structure suggested by @junpenglao

I think a bit more explanatory test would make this super!

[junpenglao]

Thanks for the effort :) hope you can contribute next time.