Lifelines

- removes `include_likelihood` from `CoxPHFitter.fit` - it was not slowing things down much (empirically), and often I wanted it for debugging (I suppose others do too). It's also another exit condition, so we many exit from the NR iterations faster.
- added `step_size` param to `CoxPHFitter.fit` - the default is good, but for extremely large or small datasets this may want to be set manually.
- added a warning to `CoxPHFitter` to check for complete seperation: https://stats.idre.ucla.edu/other/mult-pkg/faq/general/faqwhat-is-complete-or-quasi-complete-separation-in-logisticprobit-regression-and-how-do-we-deal-with-them/
- Additional functionality to `utils.survival_table_from_events` to bin the index to make the resulting table more readable.

- No longer support matplotlib 1.X
- Adding `times` argument to `CoxPHFitter`'s `predict_survival_function` and `predict_cumulative_hazard` to predict the estimates at, instead uses the default times of observation or censorship.
- More accurate prediction methods parametrics univariate models.

- Changing liscense to valilla MIT.
- Speed up `NelsonAalenFitter.fit` considerably.

- Python3 fix for `CoxPHFitter.plot`.

- fixes regression in `KaplanMeierFitter.plot` when using Seaborn and lifelines.
- introduce a new `.plot` function to a fitted `CoxPHFitter` instance. This plots the hazard coefficients and their confidence intervals.
- in all plot methods, the `ix` kwarg has been deprecated in favour of a new `loc` kwarg. This is to align with Pandas deprecating `ix`

- fix in internal normalization for `CoxPHFitter` predict methods.