Add interpreter option to allow TypeScript, modules, etc...

[gristow]

I'm wondering about the possibility of adding a --interpreter argument, specifying the absolute path to the interpreter, to allow use of, say, ts-node for executing migrations. In the project I work on that uses rethinkdb, we've been steadily converting to TypeScript, and migrations are one of the last areas where we're stuck with .js.

We might possibly also need to add an --extensions argument.

Does this seem of value?