WIP: Lean box plot option

[BioTurboNick]

Intent is to provide a visually lean version of the boxplot with a mode = :lean keyword argument, intended for for better composition with other plots e.g. dotplots. Whipped this up quickly. Suggestions welcome!

[daschw]

Could you maybe add a note about this in the boxplot section of the README?

[BioTurboNick]

@daschw - Sure I could! I want to make sure this option is desired vs. some alternative presentation, though. I'd like to let it sit for comment for a little while. Unless you love it and want it immediately haha.

[daschw]

OK sure, then let's wait a little longer for other comments and opinions.