support cross apply and outer apply

[davidAtInleague]

MSSQL Server and Oracle both support cross apply and outer apply as part of their join grammars, it would be helpful if QB offered a way to access these DB features.

An inbuilt qb.{cross,outer}Apply(...) method would be great. Alternatively a way to do something like pushRawJoin("cross apply ...") where pushRawJoin is strawman for "add the following arbitrary text into the generated sql while emitting joins" is a possible solution (issue that also discusses an 'add arbitrary sql text into specific statement positions' as a solution: #170)

An attempt, mostly a proof of concept, at adding specific {cross,outer}Apply methods is at #253

Misc. vendor info:

• Microsoft
• Oracle