Feature Request: Control zoom / text size with keyboard shortcuts

[pcgeek86]

Summary

As a user of massCode, I would like to be able to increase / decrease the font size of the application, by using de facto standard keyboard shortcuts.

CTRL + ➕ = increase text size / zoom
CTRL + ➖ = decrease text size / zoom

As of massCode version 3.1.0, these keyboard shortcuts exhibit no behavior.

[antonreshetov]

Added in #222