feat: set up project skeleton for new CLI (#1)

* docs: fill in README
* feat: initial setup of CLI, with help + version commands
* build: add linters and Makefile
* build: add initial CircleCI workflow

etc/checkfmt.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+HAS_FMT_ERR=0
+# For every Go file in the project, excluding vendor...
+for file in $(go list -f '{{$dir := .Dir}}{{range .GoFiles}}{{printf "%s/%s\n" $dir .}}{{end}}' ./...); do
+  # ... if file does not contain standard generated code comment (https://golang.org/s/generatedcode)...
+  if ! grep -Exq '^// Code generated .* DO NOT EDIT\.$' $file; then
+    FMT_OUT="$(gofmt -l -d -e $file)" # gofmt exits 0 regardless of whether it's formatted.
+    GCI_OUT="$(go run github.com/daixiang0/gci -d $file)"
+    if [[ -n "$FMT_OUT" || -n "$GCI_OUT" ]]; then
+      HAS_FMT_ERR=1
+      echo "Not formatted: $file"
+    fi
+  fi
+done
+
+if [ "$HAS_FMT_ERR" -eq "1" ]; then
+    echo 'Commit includes files that are not formatted' && \
+    echo 'run "make fmt"' && \
+    echo ''
+fi
+exit "$HAS_FMT_ERR"

etc/checktidy.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+set -e
+
+export GO111MODULE=on
+go mod tidy
+
+if ! git --no-pager diff --exit-code -- go.mod go.sum; then
+  >&2 echo "modules are not tidy, please run 'go mod tidy'"
+  exit 1
+fi