Update CI to use jobs and golangci-lint 1.23.1

[x448]

Use jobs for build, lint, coverage, and race. Use golangci-lint 1.23.1 to run linters. Update .travis.yml and create .golangci.yml with some settings for linters.

[codecov-io]

Codecov Report

Merging #11 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #11   +/-   ##
=======================================
  Coverage   60.16%   60.16%           
=======================================
  Files          15       15           
  Lines        1368     1368           
=======================================
  Hits          823      823           
  Misses        362      362           
  Partials      183      183

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