Add option to interpret size option as icon height rather than font size

[pepijnve]

@jessedoyle here's a first attempt at the change we were discussing in #62.

[jessedoyle]

Thanks for this contribution @pepijnve!

I took a bit of a deep dive and came to the same conclusion as you did. Ultimately the font metrics in the v6 files result in different rendering behaviour when compared to v5 (in particular due to more dramatic max ascender/descender values).

Added a couple of suggestions in the review, but I think the solution here is rather elegant. We'll need to add test coverage of the new option, but I'm on board with the change 👍

[pepijnve]

@jessedoyle what's still missing is documentation. I'm not all that familiar with Ruby documentation conventions so I wasn't sure what the most appropriate place would be to add something. Currently the options hash isn't really documented; it just refers to Prawn's text options.

[jessedoyle]

Hey @pepijnve - thanks for the patience on this (I was away for a few days). With respect to the documentation, I have some housekeeping changes for the next release coming in the future and can add some basic docs at that time.

I plan on merging this work shortly and will cut a release including it in the near future.

[jessedoyle]

Thanks again!

[jessedoyle]

This change has been included in the 4.1.0 version release - thanks!