GROUP BY bool_and, bool_or, stddev_samp, stddev_pop, var_samp, var_pop
merge georgewfraser: GROUP BY bool_and, bool_or, stddev_samp, stddev_pop, var_samp, var_pop

Merge pull request #154 from fivetran/sql-parser/group-by
https://github.com/FoundationDB/sql-parser/pull/154