Add versioning of interface

[ingenthr]

N1QL has laid out a versioning approach that may be worth considering here:
https://docs.google.com/document/d/1Uyv4t06DNGq7TxJjGI_T_MbbEYf8Er-imC7yzTY0uZw/edit#heading=h.x2b1nkw2rstt

[steveyen]

Thanks @ingenthr -- that gives some hope that there can be existing code to reuse somehow!

[steveyen]

see also: https://issues.couchbase.com/browse/MB-17012