add vendoring

vendor/github.com/raja/argon2pw/README.md

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+# argon2pw
+[![GoDoc](https://godoc.org/github.com/raja/argon2pw?status.svg)](https://godoc.org/github.com/raja/argon2pw)
+[![Build Status](https://travis-ci.org/raja/argon2pw.svg?branch=master)](https://travis-ci.org/raja/argon2pw)
+[![Go Report Card](https://goreportcard.com/badge/github.com/raja/argon2pw)](https://goreportcard.com/report/github.com/raja/argon2pw)
+
+Argon2 password hashing package with constant time hash comparison
+
+**Preface:**
+Argon2 was selected as the winner of the [Password Hashing Competition](https://password-hashing.net/). Argon2 is ideal for deriving cryptographic keys from passwords.
+
+This package utilizes the Argon2i hashing algorithm that is the side-channel resistant version of Argon2. It uses data-independent memory access, which is preferred for password hashing and password-based key derivation. Argon2i requires more passes over memory than Argon2id to protect from trade-off attacks.
+
+The generated salted hash is ideal for persistent storage in a single column as a string and is future proof if time or memory parameters for argon2i change.
+
+Additionally, argon2pw includes a function for password comparison in constant time to prevent [timing attack](https://en.wikipedia.org/wiki/Timing_attack) vectors.
+
+**Usage:**
+```go
+package main
+import "github.com/raja/argon2pw"
+
+ func main() {
+	 // Generate a hashed password
+	 testPassword := `testPassword$x1w432b7^`
+	 hashedPassword, err := argon2pw.GenerateSaltedHash(testPassword)
+	 if err != nil {
+         log.Panicf("Hash generated returned error: %v", err)
+	 }
+
+	 // Test correct password in constant time
+	 valid, err := argon2pw.CompareHashWithPassword(hashedPassword, testPassword)
+	 log.Printf("The password validity is %t against the hash", valid)
+
+	 // Test incorrect password in constant time
+	 valid, err = argon2pw.CompareHashWithPassword(hashedPassword, "badPass")
+	 log.Printf("The password validity is %t against the hash", valid)
+ }
+
+```