The S-1 contains a table with number of options granted as well as strike price on various dates since June 20, 2014. Some other data can be determined from the option grants for executives. Here's a rough list:
Date Strike ($)
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July 25, 2012 2.73
May 31, 2013 2.90
August 27, 2013 3.33
February 27, 2014 7.25
June 20, 2014 8.23
August 16, 2014 9.11
December 17, 2014 10.06
March 20, 2015 11.28
May 14, 2015 13.09
June 17, 2015 13.94
July 9, 2015 14.81
August 11, 2015 15.25
September 16, 2015 15.39