A general Autocomplete for the editor

[Bios-Marcel]

Currently the editor offers autocomplete only for mentions. It'd be optimal if that autocomplete would be completely dynamic, allowing the programmer to register arbitrary autocomplete patterns.

For example:

editor.RegisterAutoCompletePattern(":(.*?)(?:$|\s)", func(input string) []string) {
    return emojis.GetEmojisStartingWith(input)
})

Where the first parameter is a regular expression containing a single captured group or no captured group, resulting in the complete content being passed. The input then gets passed to the handler function, which returns the autocomplete options for that given input.

The editor would then update the view after calling the handler.

On selection another handler should be called, something like:

editor.RegisterAutoCompleteActionHandler(func (selected string) string {
  //Code  
})

The autocomplete input should always be the first match and cut off at the current cursor position.

So :Emo(Cursor)ji: would be passed as Emo and the replacement should be Replacementji.