Ace-Diff proof of concept

[dometto]

A proof of concept for merge functionality using the ace-diff library. Run gollum with --development-assets, open an editor, and execute the following JS for a very basic diff view:

$('#gollum-editor-body-ace').toggle()
const differ = new AceDiff({
  element: '.acediff',
  left: {
    content: window.ace_editor.getSession().getValue(),
  },
  right: {
    content: 'your second file content here',
  },
});
myopts = window.ace_editor.getOptions()
differ.getEditors().left.setOptions(myopts)

[dometto]

Note: this is meant primarily to store and share info about how to get ace-diff up and running, this is very far from being a real PR. :)