Plan for GHC 8.6.1

[Ryan Scott]

I have one major feature planned: -XDerivingVia. I haven't made a
patch yet, since the idea itself is still technically going through
the proposal process at [1]. But the feedback seems pretty positive,
so I think I'll submit it to the committee next week for final
consideration.

There is an implementation that's 99% already at [2], so there
shouldn't be much of a delay in getting it to Phabricator once the
committee gives the go-ahead.

Ryan S.
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[1] https://github.com/ghc-proposals/ghc-proposals/pull/120
[2] https://github.com/RyanGlScott/ghc/tree/deriving-via-8.5