Add support to readonly

[elalienx]

Hi, thanks for the library. I would like to know if there is a way to make the editor read only after initial setup. Thank in advance.

[kazzkiq]

CodeFlask already supports it via .enableReadonlyMode() and disableReadonlyMode() methods (details on #85).

e.g.:

import CodeFlask from 'codeflask';

const flask = new CodeFlask('#my-selector', { language: 'js' });

// Now your editor is read-only
flask.enableReadonlyMode();

// Now it's available for editing again
flask.disableReadonlyMode();