Add ability to specify editor for `new-entry`

[brass75]

Currently the new-entry command opens the default editor based on the environment variable EDITOR. For a variety of reasons we should add the option to specify the editor used via both the command line (and yes, I know we can do EDITOR=<editor> render-engine new-entry in Nix OSes including Mac but I don't think that works for Windows) and via the pyproject.toml

[brass75]

Fixed in $18