Update Survival Analysis intro.rst

Fixed a small typo in survival function section
Merge pull request #83 from anmolgarg/patch-1

Update Survival Analysis intro.rst
fixing inconsistent output in predict_percentiles; making tests more statistically friendly
other predictors output pd structures, this doesn't. Change it so it does
Merge pull request #84 from CamDavidsonPilon/minor-bump-to-4.3.1

fixing inconsistent output in predict_percentiles; making tests more sta...
new sort test + autolinting
Fixed typo
Merge pull request #85 from JonathanSeguin/patch-1

Fixed typo
Predicting with CoxPH could raise an error

Fixes an issue where CoxPH would cause an error to be raised
which seemed to be due to mixing of pandas and numpy.

Signed-off-by: Jonas Kalderstam <jonas@kalderstam.se>
Add tests for CoxPH which are currently failing

Noticed some strange behavior with CoxPH. I always have
normalized data, which did not seem to work good with
the implementation. The failures here seem unrelated to that
though.

The added tests currently fail with the following trace:

>Traceback (most recent call last):
>  File "/home/jonas/workspacepython/lifelines/lifelines/tests/test_suite.py", line 937, in test_crossval_normalized
>    event_col='E', k=3)
>  File "/home/jonas/workspacepython/lifelines/lifelines/utils.py", line 311, in k_fold_cross_validation
>    fitter.fit(training_data, duration_col=duration_col, event_col=event_col)
>  File "/home/jonas/workspacepython/lifelines/lifelines/estimation.py", line 998, in fit
>    include_likelihood=include_likelihood)
>  File "/home/jonas/workspacepython/lifelines/lifelines/estimation.py", line 938, in _newton_rhaphson
>    delta = solve(-hessian, step_size * gradient.T)
>  File "/home/jonas/anaconda3/lib/python3.4/site-packages/numpy/linalg/linalg.py", line 381, in solve
>    r = gufunc(a, b, signature=signature, extobj=extobj)
>  File "/home/jonas/anaconda3/lib/python3.4/site-packages/numpy/linalg/linalg.py", line 90, in _raise_linalgerror_singular
>    raise LinAlgError("Singular matrix")
>numpy.linalg.linalg.LinAlgError: Singular matrix

However, note that I have commented out one of the datasets because that
seems to cause the cross-validation to end up in an infinite loop of
some kind. The tests never finish (only waited for ~2 minutes).

Doing similar checks with *R* works with no problem.

Doing the following is a fast way to check the results:

    python -m unittest lifelines.tests.test_suite.CoxRegressionTests

Signed-off-by: Jonas Kalderstam <jonas@kalderstam.se>
fixing inequality bug, and adding noise to tests
fix typo
adding predict method to fitters, and cleaning up some tests + adding more regression tests; adding new datasets
fixing coxph prediction values
fixing a few tets
Change to gaussian noise, increase limits

Cox should really solve the data (cindex > 0.9). This
is what happens in R.

Signed-off-by: Jonas Kalderstam <jonas@kalderstam.se>
reverting the keyword argument for birth_col, I found a better way
getting baseline survival for CoxPH correct! Adding new baseline pieces like cumulative_hazard_ and baseline_survival_
adding new CoxPH test for p-values and se
make test more liberal