Added group()
group() by null should throw error, use existing method for lambda
Added cstr param to enable simple stream trace logs
Fixed typo in group() comments
Revert 98c02df..a9f8bb6

This rolls back to commit 98c02df24477353de1f5ef13b55c1d014020666c.
Fixed typo in group() docs
Merge pull request #31 from DveMac/master

Added group()