Remove gometalinter and add golangci-lint

[gssbzn]

Since there's no progress going on #120 this tries to solve the same problem with a different approach

• Mainly not installing golangci-lint as a mod dependency (something they even don't recommend doing)
• Some missing linters that are not enable by default and were being used by the project
• Some fixes flagged by running the new linter, mostly ignoring some already ignored errors

[codecov[bot]]

Codecov Report

Merging #128 into master will not change coverage. The diff coverage is 5.4%.

@@           Coverage Diff           @@
##           master     #128   +/-   ##
=======================================
  Coverage   30.45%   30.45%           
=======================================
  Files           6        6           
  Lines         696      696           
=======================================
  Hits          212      212           
  Misses        463      463           
  Partials       21       21

Impacted Files	Coverage Δ
screenbuf/screenbuf.go	60% <0%> (ø)	:arrow_up:
prompt.go	0% <0%> (ø)	:arrow_up:
select.go	17.24% <8.33%> (ø)	:arrow_up:

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[jbowes]

Thanks @gssbzn, this is awesome.

I'm going to resolve the conflicts, and set up the golangci prefs to match what we at Manifold use internally, then push it to master.