ORBA auxiliary functions version 1.0.0

This is the first release of auxiliary R functions ('DiMat' and 'DiGroup') for ordination regression-based approach (ORBA) described in Rydgren et al. 2018 Journal of Applied Ecology

'DiMat' creates a n-dimensional distance matrix between all study plots and 'plot group'=factor-level centroids based on their scores at ordination axes. Note that 'DiMat' requires installed R package 'vegan' to function properly (and anticipates ordinations made in 'vegan').

'DiGroup' groups the distances from the distance matrix according to 'plot group'=factor-level affiliation, facilitating the transition between the ordination- and regression-steps in ORBA.