Refactor the core of the lib (#700)

- Packages
- Isolate code used by the CLI into the package `cmd`
- (experimental) Add e2e tests for HTTP01, TLS-ALPN-01 and DNS-01, use [Pebble](https://github.com/letsencrypt/pebble) and [challtestsrv](https://github.com/letsencrypt/boulder/tree/master/test/challtestsrv) 
- Support non-ascii domain name (punnycode)
- Check all challenges in a predictable order
- No more global exported variables
- Archive revoked certificates
- Fixes revocation for subdomains and non-ascii domains
- Disable pending authorizations
- use pointer for RemoteError/ProblemDetails
- Poll authz URL instead of challenge URL
- The ability for a DNS provider to solve the challenge sequentially
- Check all nameservers in a predictable order
- Option to disable the complete propagation Requirement
- CLI, support for renew with CSR
- CLI, add SAN on renew
- Add command to list certificates.
- Logs every iteration of waiting for the propagation
- update DNSimple client
- update github.com/miekg/dns

acme/api/service_test.go

@@ -0,0 +1,56 @@
+package api
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_getLink(t *testing.T) {
+	testCases := []struct {
+		desc     string
+		header   http.Header
+		relName  string
+		expected string
+	}{
+		{
+			desc: "success",
+			header: http.Header{
+				"Link": []string{`<https://acme-staging-v02.api.letsencrypt.org/next>; rel="next", <https://acme-staging-v02.api.letsencrypt.org/up?query>; rel="up"`},
+			},
+			relName:  "up",
+			expected: "https://acme-staging-v02.api.letsencrypt.org/up?query",
+		},
+		{
+			desc: "success several lines",
+			header: http.Header{
+				"Link": []string{`<https://acme-staging-v02.api.letsencrypt.org/next>; rel="next"`, `<https://acme-staging-v02.api.letsencrypt.org/up?query>; rel="up"`},
+			},
+			relName:  "up",
+			expected: "https://acme-staging-v02.api.letsencrypt.org/up?query",
+		},
+		{
+			desc:     "no link",
+			header:   http.Header{},
+			relName:  "up",
+			expected: "",
+		},
+		{
+			desc:     "no header",
+			relName:  "up",
+			expected: "",
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			link := getLink(test.header, test.relName)
+
+			assert.Equal(t, test.expected, link)
+		})
+	}
+}