Interactive mode

[sleberknight]

Add an interactive mode that prompts for input.

Maybe also let the user stay in interactive mode and continue generating release notes for additional repositories. Maybe a multi-level menu system, with the first level options being to select a repository or quit, and if the user selects to generate release notes it goes into prompt mode. Once done it could then return to the top-level menu.

A few more top level options could be to view and edit configuration properties.

Interactive mode should also permit overriding and/or adding to the defaults from the config file (if it exists).

[sleberknight]

This should be added after moving the library to 1.0.0. It is not an essential feature, though it will be a nice-to-have.