Clarify the return values for SSL_read_ex()/SSL_write_ex()

=head1 RETURN VALUES

SSL_read_ex() and SSL_peek_ex() will return 1 for success or 0 for failure. In

the event of a failure call SSL_get_error() to find out the reason.

SSL_read_ex() and SSL_peek_ex() will return 1 for success or 0 for failure.

Success means that 1 or more application data bytes have been read from the SSL

connection. Failure means that no bytes could be read from the SSL connection.

Failures can be retryable (e.g. we are waiting for more bytes to

be delivered by the network) or non-retryable (e.g. a fatal network error). In

the event of a failure call L<SSL_get_error(3)> to find out the reason and if

the call is retryable or not.

For SSL_read() and SSL_peek() the following return values can occur:

=head1 RETURN VALUES

SSL_write_ex() will return 1 for success or 0 for failure. In the event of a

failure call SSL_get_error() to find out the reason.

SSL_write_ex() will return 1 for success or 0 for failure. Success means that

all requested application data bytes have been written to the SSL connection or,

if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1 application data byte has

been written to the SSL connection. Failure means that not all the requested

bytes have been written yet (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or

no bytes could be written to the SSL connection (if

SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be retryable (e.g. the

network write buffer has temporarily filled up) or non-retryable (e.g. a fatal

network error). In the event of a failure call L<SSL_get_error(3)> to find out

the reason and if the call is retryable or not.

For SSL_write() the following return values can occur: