msgpack: add benchmarks

[zchee]

Add benchmarks to the msgpack package.

Update: #94

[codecov]

Codecov Report

Merging #93 (5e3939f) into master (3b7d3b9) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master     #93   +/-   ##
======================================
  Coverage    62.8%   62.8%           
======================================
  Files          14      14           
  Lines        2081    2081           
======================================
  Hits         1308    1308           
  Misses        636     636           
  Partials      137     137           

Flag	Coverage Δ
linux-1.13	62.8% <100.0%> (ø)
linux-1.14	62.8% <100.0%> (ø)
linux-1.15	62.8% <100.0%> (ø)
linux-1.16	62.8% <100.0%> (+<0.1%)	⬆️
macos-1.13	62.8% <100.0%> (+<0.1%)	⬆️
macos-1.14	62.8% <100.0%> (+<0.1%)	⬆️
macos-1.15	62.8% <100.0%> (ø)
macos-1.16	62.8% <100.0%> (ø)
windows-1.13	62.0% <100.0%> (ø)
windows-1.14	62.0% <100.0%> (ø)
windows-1.15	62.0% <100.0%> (ø)
windows-1.16	62.0% <100.0%> (+<0.1%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
msgpack/msgpack.go	66.6% <ø> (ø)
msgpack/pack.go	87.5% <100.0%> (ø)
msgpack/unpack.go	90.6% <100.0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3b7d3b9...5e3939f. Read the comment docs.