George Barnett authored Jun 04, 2020 and Nathan Harris committed Jun 04, 2020

Motivation:

SET has a range of options for setting expirations and conditionally
setting a value.

Modification:

- Add another `set` function with a range of options. Options are
  modelled as `struct`s backed by private `enum`s to allow additional
  options to be added without breaking API.
- Added tests

Result:

Options may be specified with `set`, and resolves #67