v0.13.2

First pre-release. Most of package core functionality is in place and API is semi-stable

Features:

• Cox model
• Aalen-Johansen
• Kaplan-Meier
• Late entry
• Right censoring
• use of @formula interface from StatsAPI

Still in the works:

• Robust variance estimator
• Interface with Optimizer if default Newton-Raphson approach does not work