Optimistic locking

[cur3n4]

Rough attempt at implementing optimistic locking.

[neumino]

Sounds reasonable to me, the current implementation seems to be working. I would have two little questions:

• Can we find a better name than optimisticLocking?
• How does this field version plays with the schema? I guess you have to declare it like type.number()?

[cur3n4]

• How about the name version? This is the standard in the JAVA world.
• My suggestion would be to support different types and the type defines the way to generate the next version value . type.number() will behave as an auto increment field, type.string() as an uuid and type.date() as a timestamp.

I'll prepare a proper PR.

[cur3n4]

Sorry for the delay, I have updated the PR.
Renamed configuration option to version. I have included support for columns of type Date and Number . Strings are doable also but will require either adding support to generate UUID or use r.uuid().
Please let me know your thoughts.