Could not set size lesser than certain value

https://github.com/imsky/holder/blob/5d03b972f0082c6c640f8e9223ca897ebc24dd50/src/lib/index.js#L844

This code use image dimensions and `App.defaults.scale` which is not configurable for fontSize computing. https://github.com/imsky/holder/blob/5d03b972f0082c6c640f8e9223ca897ebc24dd50/src/lib/index.js#L660

Hence font size could not be lesser then some computed value. It would be great to set any font size.

Start in src/lib/index.js at the referenced lines around 660 and 844. Trace how image dimensions and App.defaults.scale are used when computing fontSize, then run the existing test suite to establish current behavior. Done means the font-size calculation permits values smaller than the current computed minimum, with relevant behavior covered by tests.

Written by the indexing model from the issue text.