Add grpclog.LoggerV2 logger

[kazegusuri]

Fixed V() implementation based on #538.

Official grpclog.LoggerV2 implementation sets verbose level at initialization. So I adopt functional option to set verbose level.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #613 into master will decrease coverage by 0.15%.
The diff coverage is 88.57%.

@@            Coverage Diff             @@
##           master     #613      +/-   ##
==========================================
- Coverage   97.38%   97.23%   -0.16%     
==========================================
  Files          40       40              
  Lines        2102     2132      +30     
==========================================
+ Hits         2047     2073      +26     
- Misses         47       51       +4     
  Partials        8        8

Impacted Files	Coverage Δ
zapgrpc/zapgrpc.go	93.22% <88.57%> (-6.78%)	⬇️

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[AlekSi]

@frankgreco please sign CLA. That should take only a few minutes.

[frankgreco]

@AlekSi

It seems that I have already signed the CLA.

You can verify from the username in that image and the username from my commits in this PR that they are the same.

Maybe we should get a repo admin involved?

[kazegusuri]

nothing happened by repush

[AlekSi]

@frankgreco You should add the email address from commit to your GitHub profile.

[kazegusuri]

codecov check failed, but test and cla passed. PTAL.

[kazegusuri]

what the status?

[frankgreco]

@kazegusuri

#538 (comment)

[kazegusuri]

I modified with your latest commit, then the cla check passed!

[ZackButcher]

Fixes #534.

[zchee]

Is there any progress?

/cc @akshayjshah

[frankgreco]

I believe this is done. Just waiting for a review.

[vvakame]

👀

[at-ishikawa]

Is there any progress so far?
I really want this PR to be merged.