Add forgotten AppendBinary to ArrayEncoder

[NWilson]

For some reason, ObjectEncoder has AddBinary and AddByteString methods, but ArrayEncoder only has AppendByteString. This PR adds the missing (forgotten?) AppendBinary method.

I realise this will have to wait until zap v2, since it's a breaking API change.

[codecov]

Codecov Report

Merging #669 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #669   +/-   ##
=======================================
  Coverage   97.38%   97.38%           
=======================================
  Files          40       40           
  Lines        2102     2105    +3     
=======================================
+ Hits         2047     2050    +3     
  Misses         47       47           
  Partials        8        8           

Impacted Files	Coverage Δ
zapcore/encoder.go	83.13% <ø> (ø)
zapcore/json_encoder.go	100.00% <100.00%> (ø)
zapcore/memory_encoder.go	98.68% <100.00%> (+0.01%)	⬆️

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[NWilson]

Ping - could you create a "v2-unstable" branch (or similar) where API breaking changes can be merged that will go into the v2 release, whenever it is? Otherwise without a branch, any future improvements can't be developed.

[CLAassistant]

All committers have signed the CLA.

[prashantv]

We've been tracking improvements in #388

I'd suggest leaving a comment linking to this PR in that task as we're not currently maintaining a v2 branch.