support for long.js

[lishengguo]

writeLong(Long.fromValue(7))

[mention-bot]

@lishengguo, thanks for your PR! By analyzing the history of the files in this pull request, we identified @fengmk2, @gxcsoccer and @xusiyuan841028 to be potential reviewers.

[codecov[bot]]

Codecov Report

Merging #85 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff           @@
##           master     #85   +/-   ##
======================================
  Coverage    96.1%   96.1%           
======================================
  Files           7       7           
  Lines        1079    1079           
  Branches      204     204           
======================================
  Hits         1037    1037           
  Misses         42      42

Impacted Files	Coverage Δ
lib/v2/encoder.js	94.57% <100%> (ø)	:arrow_up:

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[fengmk2]

any test cases?

[lishengguo]

add test case : Long.fromNumber(0)

[fengmk2]

Please rebase from master branch.