[WIP] Add functions for working with interleaved experiments
- C++-based exact_binomial() to estimate sample size for exact binomial tests
- Functions for working with interleaved search results experiments; see ?interleaved for details
- interleaved_preference() calculates the preference statistic from click data according to Eq. 4 from Chapelle et al. (2012) paper on interleaved search evaluation
- ggplot themes theme_min() and theme_facet()
- Documentation updates
- Syntax-checking unit test
Bug: T150032
Change-Id: Ie6aa90fad2b25a07b200a2c822f5a34227cca8c8