v0.7: scheduled release

• Dict\flatten by Kunal Mehta on 2017-10-09
• Keyset\gen by Kunal Mehta on 2017-10-09
• Remove Str\join_args_switched by Kunal Mehta on 2017-10-08
• Str{join_args_switched -> join} by Kunal Mehta on 2017-10-06