[VOTE] C++14 Upgrade

[Michael Park]

I'm going to put this up for a vote. My plan is to bump us to C++14 on Feb
21.

The following are the proposed changes:
  - Minimum GCC *4.8.1* => *5*.
  - Minimum Clang *3.5* => *3.6*.
  - Minimum Apple Clang *8* => *9*.

We'll have a standard voting, at least 3 binding votes, and no -1s.

Thanks!

MPark