Refactor api (#6)

* Refactor library, remove duplicates

* Rebuild structure to use Messages and Signature models

* Use PGPSplitMessage

* Remove signature model

* Various fixes

* Add helpers with tests

* Fixes, add some docs, add tests

* Add attachment helpers

* Add helpers Symmetric encryption

* Edit docs + examples

* Rename kr to keyRing

* Various fixes for documentation

* Edit JSON handling functions, add decrypt keyring via token

* Add proposal changes doc

* Fix CI

* Drop *Message functions, join CleartextMessage and BinaryMessage

* Change canonicalization and trimming only to text signatures

* Add cleartextsignature, detach signature from message model, move helpers

* Documentation, remove optional parameters

* Move verification to separate model

* Don't return message in VerifyDetached

* Update table of contents in readme

* Appease golint

* Run go fmt

* Rename Encrypt/DecryptMessageWithPassword to ..WithToken

These functions shouldn't be used with user-provided passwords,
as they don't do any key-stretching.

* Change key generation usernames

helper/cleartext_test.go

@@ -0,0 +1,45 @@
+package helper
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const signedPlainText = "Signed message\n"
+const testTime = 1557754627 // 2019-05-13T13:37:07+00:00
+var signedMessageTest = regexp.MustCompile(
+	"(?s)^-----BEGIN PGP SIGNED MESSAGE-----.*-----BEGIN PGP SIGNATURE-----.*-----END PGP SIGNATURE-----$")
+
+func TestSignClearText(t *testing.T) {
+	// Password defined in base_test
+	armored, err := SignCleartextMessageArmored(
+		readTestFile("keyring_privateKey", false),
+		testMailboxPassword,
+		signedPlainText,
+	)
+
+	if err != nil {
+		t.Fatal("Cannot armor message:", err)
+	}
+
+	assert.Regexp(t, signedMessageTest, armored)
+
+	verified, err := VerifyCleartextMessageArmored(
+		readTestFile("keyring_publicKey", false),
+		armored,
+		pgp.GetUnixTime(),
+	)
+	if err != nil {
+		t.Fatal("Cannot verify message:", err)
+	}
+
+	assert.Exactly(t, canonicalizeAndTrim(signedPlainText), verified)
+}
+
+func TestMessageCanonicalizeAndTrim(t *testing.T) {
+	text := "Hi  \ntest!\r\n\n"
+	canon := canonicalizeAndTrim(text)
+	assert.Exactly(t, "Hi\r\ntest!\r\n\r\n", canon)
+}