pre-select the last run example for a crate

[rnag]

It would be nice to pre-select the last-run example on a per crate basis, whenever rx is invoked without arguments.

For instance, if the last run example was my_example and the arguments passed to the example were --my-arg test, then in the selection list that gets displayed when rx is run without arguments, it would be nice to pre-select my_example from the list of available examples for the crate; and the same arguments from last time should be passed in to the example when a user confirms the selection with the Enter key.