SSL.State: The AEAD length field is gone in TLS 1.3.
Document rsa_unpad return value.
Removed support for non-fPic-compiled libgcc on 1997-era Solaris.
p is always larger than 2. Don't add 1.
Some bugfixes and optimizations of small_factor().
SSL.File: Propagate fatal alerts to close and write callbacks.

SSL did not call the close_callback on SSL.File()s that connect outgoing
and abort the handshake by sending fatal alerts to the server.

Fatal alerts generated locally (ie due to broken data from peer)
are now signalled on the close and write callbacks with errno set
to ECONNABORTED and fatal alerts received from the peer have errno
set to ECONNRESET.

Thanks to Tobias S. Josefowitz <tobij@tobij.de> for the report.

Tentative fix for [LysLysKOM 21005266].
Require GMP 4.0 or newer to be installed.
UX improvements.
The PRIME_LIMIT is assumed to be 1024 in other parts of the code. Make it constant.