v0.4.0: Methodological and infrastructure improvements

[zsusswein]

Goal

Additional basic package functionality, performance improvements, and fixes in response to user testing.

Features

• Data simulator: delay process
• Consider defaulting to mh posterior_samples arguement rather than gaussian.  #95
• Data simulator: case curve from specified Rt time series #96
• Summary method #68
• User feedback on input data formatting #15
• Investigate diagnostic thresholds and warnings #29
• Explore alternative penalty basis dimensionality defaults #19