added golangci linter; code cleanup

.golangci.yaml

@@ -0,0 +1,75 @@
+linters-settings:
+  dupl:
+    threshold: 100
+  goconst:
+    min-len: 3
+    min-occurrences: 4
+  gocritic:
+    enabled-tags:
+      - diagnostic
+      - experimental
+      - opinionated
+      - performance
+      - style
+    disabled-checks:
+      - whyNoLint
+      - filepathJoin
+  gomnd:
+    checks:
+      - argument
+      - case
+      - condition
+      - return
+    ignored-numbers:
+      - '0'
+      - '1'
+      - '2'
+      - '3'
+      - '4'
+      - '5'
+    ignored-functions:
+      - strings.SplitN
+      - os.OpenFile
+      - os.MkdirAll
+      - os.WriteFile
+  govet:
+    check-shadowing: false
+  lll:
+    line-length: 140
+  misspell:
+    locale: US
+  nolintlint:
+    allow-unused: false # report any unused nolint directives
+    require-explanation: false # don't require an explanation for nolint directives
+    require-specific: false # don't require nolint directives to be specific about which linter is being skipped
+
+linters:
+  disable-all: true
+  enable:
+    - bodyclose
+    - depguard
+    - dogsled
+    - dupl
+    - errcheck
+    - exportloopref
+    - gochecknoinits
+    - gocritic
+    - gofmt
+    - gomnd
+    - goprintffuncname
+    - gosec
+    - gosimple
+    - govet
+    - lll
+    - misspell
+    - nakedret
+    - noctx
+    - nolintlint
+    - staticcheck
+    - stylecheck
+    - typecheck
+    - unconvert
+    - unparam
+    - unused
+    - whitespace
+