implement randomize_order and repetitions opts
implement randomize_order and repetitions opts

closes issue #70

wolfgangwalther/jsPsych,msrresearch/jsPsych,jspsych/jsPsych,shamrt/jsPsych,adrianoesch/jsPsych,Scienthusiast/jsPsych,jodeleeuw/jsPsych,andyh616/jsPsych,Scienthusiast/jsPsych,shamrt/jsPsych,erikasf/jsPsych,vergenzt/jsPsych,vergenzt/jsPsych,erikasf/jsPsych,wolfgangwalther/jsPsych,adrianoesch/jsPsych,andyh616/jsPsych,jspsych/jsPsych,jspsych/jsPsych,jspsych/jsPsych