Support Group By

[worldspawn]

• Apply to expression parser
• Apply to query api
• Apply to language processors

[worldspawn]

I think the querytable can be extended to support this. Eg:

queryTable.GroupBy(() => someTable.Foo, () => queryTable.Bar);

QueryTable<TEntity> GroupBy(params Expression<Func<object>>[] groupByExpressions)

Using group by should automatically make a query table a subquery. It might also make sense to provide a similar method on Projection or make it part of the projection creation process where currently you pass a series of columns to map but you can also optionally provide a set of group by expressions to apply to the underlying query.