Introduce covimerage for test coverage

[haya14busa]

https://github.com/Vimjas/covimerage

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@e02173c). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #73   +/-   ##
=========================================
  Coverage          ?   66.92%           
=========================================
  Files             ?        1           
  Lines             ?     3589           
  Branches          ?        0           
=========================================
  Hits              ?     2402           
  Misses            ?     1187           
  Partials          ?        0

---

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 e02173c...1a884b9. Read the comment docs.

[haya14busa]

@mattn can you review this p-r?

[mattn]

👍