Add support for custom command completion in the annotation method of command registration

[EDawg878]

This fork is tested and verified to be working, it does not break previous versions of Intake.

Example Usage:

ParametricBuilder builder = new ParametricBuilder();
builder.addCompleter(new ExampleCommand());

public class ExampleCommand implements CommandCompleter {

  @Command(aliases="example", desc="example", completer=ExampleCommand.class)
  public void example() {
     //example command
  }
  @Override
  public List<String> getSuggestions(String arguments, CommandLocals locals) throws CommandException {
    // add custom command completion implementation
  }
}