0.6.0

Added new association test normalisr.association.association_test_5 that uses given mask to determine X-Y pairs in hypothesis tests with multi-variate regression. This option is not yet available on command line.
Refactored normalisr.association, normalisr.de, and normalisr.coex.
Added option 'lowmem' to reduce memory footprint by not returning regression coefficients of covariates.