Update `toBinomialExact()`

[keaven]

Add capability to produce updated bounds at interim analysis.
This requires addition of the following optional arguments with NULL default values:

1. events - a vector with the number of observed events at each analysis
2. alpha - alpha level that may differ from input design; useful for graphical methods or for repeated/sequential p-value and confidence intervals
3. usTime - optional vector to define spending time at each analysis for upper bound
4. lsTime - optional vector to define spending time at each analysis for lower bound

Help file and vignette will need updating. Also writing a section for technical manual.

[LittleBeannie]

Move to Q4