Lifelines

New features
- `find_best_parametric_model` can handle left and interval censoring. Also allows for more fitting options.
- `AIC_` is a property on parametric models, and `AIC_partial_` is a property on Cox models.
- `penalizer` in all regression models can now be an array instead of a float. This enables new functionality and better
control over penalization. This is similar (but not identical) to `penalty.factors` in glmnet in R.
- some convergence tweaks which should help recent performance regressions.

New features
- At the cost of some performance, convergence is improved in many models.
- New `lifelines.plotting.plot_interval_censored_lifetimes` for plotting interval censored data - thanks sean-reed!

Bug fixes
- fixed bug where `cdf_plot` and `qq_plot` were not factoring in the weights correctly.

New features
- `plot_lifetimes` accepts pandas Series.

Bug fixes
- Fixed important bug in interval censoring models. Users using interval censoring are strongly advised to upgrade.
- Improved `at_risk_counts` for subplots.
- More data validation checks for `CoxTimeVaryingFitter`

Bug fixes
- Improved stability of interval censoring in parametric models.
- setting a dataframe in `ancillary_df` works for interval censoring
- `.score` works for interval censored models

New features
- new `logx` kwarg in plotting curves
- PH models have `compute_followup_hazard_ratios` for simulating what the hazard ratio would be at previous times. This is useful because the final hazard ratio is some weighted average of these.

Bug fixes
- Fixed error in HTML printer that was hiding concordance index information.

Bug fixes
- Fixed bug when no covariates were passed into `CoxPHFitter`. See 975
- Fixed error in `StatisticalResult` where the test name was not displayed correctly.
- Fixed a keyword bug in `plot_covariate_groups` for parametric models.