0.16.0

Upgrading Bouncy Castle to version 1.84.
SSL non-blocking I/O improvements.

• [feat] implement OpenSSL::ASN1.traverse helper
• [feat] remove SHA1PRNG fallback: use default SecureRandom
• [fix] SSL write loss on non-blocking partial flush (#242)
• [fix] read_nonblock(exception: false) raising SSLErrorWaitReadable
• [fix] X509::Certificate#dup dropping all extensions (#356)
• [fix] format authorityInfoAccess extension values (#210)
• [fix] coerce HMAC#update input as String
• [compat] undefine clone on Store and StoreContext
• [refactor] use constant-time comparison in PKCS7 and SimpleSecretKey
• [refactor] overflow protection in MemBIO buffer reallocation
• [deps] upgrade BC to version 1.84