Allow setting individual keys using CLI YAML style pairings

[Cducharme84]

With Metron-Tagger being the current only tool that writes MetronInfo.xml having the ability to set key-pairs would make migrations easier.

Specific use case is for issues that are tagged with the volume as start year within their ComicInfo.xml usually for accommodation of an ingesting program, these are correctly identifying those start years as start years and are naturally not entering in a volume as there wouldn't be one present in the original metadata being migrated from. This leaves the user with a MetronInfo.xml without a volume and no way to manually set this without direct editing of the archive's .xml.

To be clear, not suggesting any logics to automatically place a volume number as that's a fool's errand with some comics having so many scattered volumes but just provide the ability to manually set using the tool.

I'm sure there will be other key pairs identified as useful as well, but this is the only one I see as being an immediate need once there's ingesting programs.

For reference I've included the command like that the tool comicbox (from AJ) utilizes for writing individual keys, setting multiple here just to provide a potential syntax example.

comicbox -w "Series: Hatchet, Volume: 1, Number: 2, Genre: [Horror,Licensed,Comedy]"

As you can see the command line YAML is fairly simple and able to utilize comma delimited fields as well with proper bracketing.

While I personally am setting a bash script to edit the file for my manual work as it's a fairly simple process I know that the average user is less inclined to whip up custom solutions.