Add default prim implementations to further reduce boilerplate

[LaCuneta]

In looking at the Python extension code, I think there is an opportunity to slash a little more boilerplate. The Run, RunResult, and Set prims could be made more generic, taking in an appropriate lambda to execute the actual action. Or it could be an object implementing an interface. I should double-check the R and JS extensions again to make sure my intuition is correct, but I'm opening this so I don't forget.

[JamesHovet]

Maybe its because I just read an article for one of my CS classes about how sometimes a little duplicated code is better than a non-universal abstraction but I think that the benefits of de-duplicating that code is less than the cost of it not necessarily fitting all use cases.

And of course you could still expose the underlying library calls but I think that I like having the one way of doing things and having the line between the client code and the library code where it is.