Lifelines

New features
- Fixed and silenced a lot of warnings

Bug fixes
- Migrate to newer Pandas `Styler` for `to_latex`

API Changes
- There were way too many functions on the summary objects, so I've hidden `to_*` on them.

Bug fixes
- Fixed issue in add_at_risk_table when there were very late entries.

New features
- all `fit_` methods now accept a `fit_options` dict that allows one to pass kwargs to the underlying fitting algorithm.


API Changes
- `step_size` is removed from Cox models `fit`. See `fit_options` above.

Bug fixes
- fixed Cox models when "trivial" matrix was passed in (one with no covariates)

Dropping Python3.6 support.

Bug fixes
- Fix late entry in `add_at_risk_counts`.

New features
- `add_at_risk_counts` has a new flag to determine to use start or end-of-period at risk counts.
- new column in fitter's `summary` that display the number the parameter is being compared against.

API Changes
- `plot_lifetimes`'s `duration` arg has the interpretation of "relative time the subject died (since birth)", instead of the old "time observed for". These interpretations are different when there is late entry.

New features
- adding `weights` to log rank functions

Bug fixes
- Fix using formulas with `CoxPHFitter.score`