add stats for average tree depth, and for number of relations.
add stats for average tree depth, and for number of relations.

virneo/relex,rodsol/relex,ainishdave/relex,virneo/relex,williampma/relex,anitzkin/relex,AmeBel/relex,rodsol/relex-temp,rodsol/relex,opencog/relex,linas/relex,leungmanhin/relex,rodsol/relex-temp,leungmanhin/relex,leungmanhin/relex,anitzkin/relex,williampma/relex,AmeBel/relex,anitzkin/relex,AmeBel/relex,rodsol/relex-temp,linas/relex,virneo/relex,rodsol/relex,rodsol/relex-temp,ainishdave/relex,opencog/relex,ainishdave/relex,opencog/relex,virneo/relex,anitzkin/relex,williampma/relex,rodsol/relex-temp,anitzkin/relex,linas/relex,rodsol/relex,williampma/relex,ainishdave/relex