Fix: error on ggs_crosscorrelation

Same problem as in issue #18: dropped dimensions.
There still remains a problem when only 1 or 2 parameters
Merge branch 'crosscorrelation' of https://github.com/jucor/ggmcmc into jucor-crosscorrelation
Thanks to jucor. Solves issue with crosscorrelation and number of dimensions.
Code arrangement.