Merge branch 'master' of https://github.com/zenexity/ReactiveMongo
Initial layout of aggregation framework

The commands are all in there, as well as converting them to a BSON doc.
Left in old code for macros
Merge branch 'master' of https://github.com/zenexity/ReactiveMongo into aggregation
Ready to review Aggregation prototype.
Forgot Scaladocs
Merge branch 'aggregation' of github.com:gatorcse/ReactiveMongo into gatorcse-aggregation
[#27] Merge and adapt PR #27: Aggregation Framework Support

Move the aggregation.scala in the driver subproject and adapt it to the new BSON library.

Closes #18
Closes #27