Organize Pinniped CLI into subcommands; Add get-kubeconfig subcommand

- Add flag parsing and help messages for root command,
  `exchange-credential` subcommand, and new `get-kubeconfig` subcommand
- The new `get-kubeconfig` subcommand is a work in progress in this
  commit
- Also add here.Doc() and here.Docf() to enable nice heredocs in
  our code

internal/here/doc.go

@@ -0,0 +1,25 @@
+/*
+Copyright 2020 VMware, Inc.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package here
+
+import (
+	"strings"
+
+	"github.com/MakeNowJust/heredoc/v2"
+)
+
+const (
+	tab        = "\t"
+	fourSpaces = "    "
+)
+
+func Doc(s string) string {
+	return strings.ReplaceAll(heredoc.Doc(s), tab, fourSpaces)
+}
+
+func Docf(raw string, args ...interface{}) string {
+	return strings.ReplaceAll(heredoc.Docf(raw, args...), tab, fourSpaces)
+}

internal/here/doc_test.go

@@ -0,0 +1,104 @@
+/*
+Copyright 2020 VMware, Inc.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package here
+
+import (
+	"testing"
+
+	"github.com/sclevine/spec"
+	"github.com/sclevine/spec/report"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDoc(t *testing.T) {
+	spec.Run(t, "here.Doc", func(t *testing.T, when spec.G, it spec.S) {
+		var r *require.Assertions
+
+		it.Before(func() {
+			r = require.New(t)
+		})
+
+		it("returns single-line strings unchanged", func() {
+			r.Equal("the quick brown fox", Doc("the quick brown fox"))
+			r.Equal("  the quick brown fox", Doc("  the quick brown fox"))
+		})
+
+		it("returns multi-line strings with indentation removed", func() {
+			r.Equal(
+				"the quick brown fox\njumped over the\nlazy dog",
+				Doc(`the quick brown fox
+						jumped over the
+						lazy dog`),
+			)
+		})
+
+		it("ignores the first empty line and the whitespace in the last line", func() {
+			r.Equal(
+				"the quick brown fox\njumped over the\nlazy dog\n",
+				Doc(`
+						the quick brown fox
+						jumped over the
+						lazy dog
+				`),
+			)
+		})
+
+		it("turns all tabs into 4 spaces", func() {
+			r.Equal(
+				"the quick brown fox\n    jumped over the\n        lazy dog\n",
+				Doc(`
+						the quick brown fox
+							jumped over the
+								lazy dog
+				`),
+			)
+		})
+	}, spec.Parallel(), spec.Report(report.Terminal{}))
+
+	spec.Run(t, "here.Docf", func(t *testing.T, when spec.G, it spec.S) {
+		var r *require.Assertions
+
+		it.Before(func() {
+			r = require.New(t)
+		})
+
+		it("returns single-line strings unchanged", func() {
+			r.Equal("the quick brown fox", Docf("the quick brown %s", "fox"))
+			r.Equal("  the quick brown fox", Docf("  the %s brown %s", "quick", "fox"))
+		})
+
+		it("returns multi-line strings with indentation removed", func() {
+			r.Equal(
+				"the quick brown fox\njumped over the\nlazy dog",
+				Docf(`the quick brown %s
+						jumped over the
+						lazy %s`, "fox", "dog"),
+			)
+		})
+
+		it("ignores the first empty line and the whitespace in the last line", func() {
+			r.Equal(
+				"the quick brown fox\njumped over the\nlazy dog\n",
+				Docf(`
+						the quick brown %s
+						jumped over the
+						lazy %s
+				`, "fox", "dog"),
+			)
+		})
+
+		it("turns all tabs into 4 spaces", func() {
+			r.Equal(
+				"the quick brown fox\n    jumped over the\n        lazy dog\n",
+				Docf(`
+						the quick brown %s
+							jumped over the
+								lazy %s
+				`, "fox", "dog"),
+			)
+		})
+	}, spec.Parallel(), spec.Report(report.Terminal{}))
+}