v0.8: scheduled release

• Unrelease C{max, max_by, min, min_by} by Kunal Mehta on 2017-10-20
• Math{maxv, minv} by Kunal Mehta on 2017-10-19
• Unrelease C{sum, sum_float} by Kunal Mehta on 2017-10-17
• Make Vec\concat optimizable by Kunal Mehta on 2017-10-17
• Make Dict\merge optimizable by Kunal Mehta on 2017-10-16
• Make Keyset\union optimizable by Kunal Mehta on 2017-10-16