eccooc (devel)

Created class pa for presence absence objets.
Implemented Rcpp counts occurrence of all pairs and all triplets/triads (see #7).
ec_rarefaction() computes rarefaction curve.
ec_betadiversity() computes a few metrics of betadiversity.
Added a NEWS.md file to track changes to the package.
ec_checkerboard() computes classical C-score (see #10).