Added generichash keygen

multiplatform-crypto-libsodium-bindings/src/commonMain/kotlin/com.ionspin.kotlin.crypto/generichash/GenericHash.kt

@@ -6,6 +6,8 @@ package com.ionspin.kotlin.crypto.generichash
  * on 21-Aug-2020
  */
 
+val crypto_generichash_BYTES = 32
+
 data class GenericHashState(val hashLength: Int, val internalState: GenericHashStateInternal)
 
 expect class GenericHashStateInternal
@@ -18,6 +20,8 @@ expect object GenericHash {
     fun genericHashUpdate(state: GenericHashState, messagePart : UByteArray)
     fun genericHashFinal(state : GenericHashState) : UByteArray
 
+    fun genericHashKeygen() : UByteArray
+
 }