* allow p % 24 == 23 when generator == 2 in DH_check

* short url

* update and expand comments

* even better language!

* No more FUNCS/MACROS distinction

* change the docs to not talk about MACROS since they're gone

* remove out of date comment

* Add PEM_write_bio_DHxparams

* Define PEM_write_bio_DHxparams only if EVP_PKEY_DHX defined.
Both added in commit afb14cda in openssl

* Add d2i_DHxparams_bio and i2d_DHxparams_bio bindings

* Fix bindings addition

* change condtional bindings to be after 1.1.0f

* Change i2d_DHxparams_bio return type

* define Cryptography_d2i_DHxparams_bio and Cryptography_i2d_DHxparams_bio

* Remove d2i_DHxparams_bio, i2d_DHxparams_bio bindings

* Add declarations for Cryptography_d2i_DHxparams_bio and Cryptography_i2d_DHxparams_bio

* Move Cryptography_d2i_DHxparams_bio and Cryptography_i2d_DHxparams_bio declaration to MACROS

* Add Cryptography_d2i_DHxparams_bio, Cryptography_i2d_DHxparams_bio and PEM_write_bio_DHxparams to _coditionals.py

* Make sure we did not define EVP_PKEY_DHX

* Attempt to simplify the libressl checing

* SHENANGINS

* Attempted fix

* More simplification

* Backport DH_check from OpenSSL 1.1.0.

OpenSSL 1.0.2's DH_check considers the q parameter, allowing it
validate more generators and primes; however, OpenSSL 1.1.0's DH_check
includes code to handle errors in BN functions, so it's preferred.

* Wrap DH_Check when using OpenSSL 1.1.0 or higher.

* Adding DH_CHECK_* values missing from older OpenSSLs

* Defensively guard DH_CHECK_* definitions with ifndef.

This will prevent duplicate definitions when LibreSSL supports a
version of DH_check that can return these.

* Document the OpenSSL of origin for the DH_check code

* Use a series of constants for OpenSSL version checks.

N.B. I removed several qualifiers that were being used to express beta vs. release in OpenSSL version numbers. Reviewers please look closely!

* Convert some python as well, also add the file

* flake8

* Simplify code, remove functionality that can be expressed more simply

* clean up the tests as well

* more constants

* wrap long lines

* reflect feedback

* unused

* add this back?

constify + a few small changes to the null checks