OX: Announce public key on PEP

src/pgp/gpg.c:p_ox_gpg_readkey

Used to read a public key from a file. The function will return the fingerprint
of the file and the base64 encoded key.

src/xmpp/ox.[hc]

ox_announce_public_key(const char* const filename) can be called from the /ox
announce <filename> command. The key within the file will be pushed on PEP and
the Metadata node will be set.

Issue: #1331

src/pgp/gpg.h

@@ -76,6 +76,8 @@ char* p_ox_gpg_signcrypt(const char* const sender_barejid, const char* const rec
 
 char* p_ox_gpg_decrypt(char* base64);
 
+void p_ox_gpg_readkey(const char* const filename, char** key, char** fp);
+
 /*!
  * \brief List of public keys with xmpp-URI.
  *