Stroke-outcome

Functions for importing mRS and utility distributions no longer return the associated notes by default.

Recalculated mRS distributions when documentation and summaries were written. These distributions are rounded to 3 decimal places and have various small differences from the previous version. The differences are mostly from changes to the excess death rates.

Most important changes:
+ Added methods for inputting patient data using a DataFrame. This removed the need for the "number of patients" argument when creating the model objects.
+ Removed the requirement to explicitly pass mRS distributions and utility weightings as input. If inputs are not given, default values are used.

Minor changes:
+ :bug: Small bug fixes for data input sanity checks. For example floats can now quietly change to integers if they're equivalent.
+ "x" value has been renamed to "fixed probability" in outcome_utilities but not yet in the notebooks in docs/.

New: discrete outcome model.