Better control over the C++ code execution.

What has changed

• Added Cauchy combination test cauchy_combined including vignette that compares combination methods
• simulate_traits now returns genotype matrix with causal epistatic variants named according to the trait they affect
• Added progress bar and possibility to interrupt C++ routine using RcppProgress
• Fixed "incorrect number of dimensions" error in simulate_traits

Full Changelog: v2.0.1...v2.0.2