End of July Release

This release contains all bugfixes from the last week and should be good to go for a wider set of databases. A known issue is that the Age at diagnosis metrics may not be populated for the target cohorts in all databases (see #68), and also some target cohorts (e.g. T4) seem to yield no results in any of the databases so far. Also, databases that are constrained to R version 3 may want to check out #73.