added binding support for rfc 5705 (#3878)

* added binding support for rfc 5705

* WIP: testing some cffi updates

* added openssl version check

* updated cffi defs to align with pep8

* removed superfluous version checks

* remove more unecessary boilerplate
diff --git a/src/_cffi_src/openssl/ssl.py b/src/_cffi_src/openssl/ssl.py
index 8bda4e0..7f9eff0 100644
--- a/src/_cffi_src/openssl/ssl.py
+++ b/src/_cffi_src/openssl/ssl.py
@@ -420,6 +420,8 @@
                                   size_t);
 size_t SSL_get_client_random(const SSL *, unsigned char *, size_t);
 size_t SSL_get_server_random(const SSL *, unsigned char *, size_t);
+int SSL_export_keying_material(SSL *, unsigned char *, size_t, const char *,
+                               size_t, const unsigned char *, size_t, int);
 
 long SSL_CTX_sess_number(SSL_CTX *);
 long SSL_CTX_sess_connect(SSL_CTX *);