Adding data check on initialisation of distribution objects
Add exponential distribution
Adding dist_pdf methods for all distributions
Adding vuongs statistic
Added population data set.
Bug fix with dist_cdf in dislnorm
Updated documentation
Bug fix in discrete lnorm pdf
1. Changing vuong -> compare_distribution
2. Added generic plot method
3. Update associated docs and tests
Minor tweaks
Roxygen tweak
Added discrete exponential
Add log argument to dist_pdf
No longer need data to set xmin and parameters
Updating documentation
Updated docs
Minor tweak to test suite
Updated documentation
Typo
Updated bootstrap data sets.