code: function findPreviousNonSpacePoint(editor, pos) {
  	const stream = new BufferStreamReader(editor.getBuffer(), pos);
  	while (!stream.sof()) {
  		if (!isSpace(stream.backUp(1))) {
  			stream.next();
  			break;
  		}
  	}
  
  	return stream.pos;
  }
docs: Finds position of first non-space character that precedes given `pos`
  @param  {TextEditor} editor
  @param  {Point} pos
  @return {Point}