starting moduli.c port from OpenSSH

dh/README

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+The functions found in this sub-component are ported almost directly from the
+openssh-portable[0]'s `moduli.c`[1] code (with, of course, changes made where
+appropriate to match and take advantage of Golang).
+
+The OpenBSD and OpenSSH(-portable) teams have my gratitude.
+
+OpenSSH/OpenSSH portable are released under a combination of the following licenses[2]:
+
+* public domain
+* "BSD-style"
+* 2-, 3-, and 4-clause BSD
+* Beerware
+
+The license in full for OpenSSH/OpenSSH-Portable can be found at [2].
+
+The license for OpenSSH-Portable's `moduli.c` is as follows:
+
+###########################################################################
+Copyright 1994 Phil Karn <karn@qualcomm.com>
+Copyright 1996-1998, 2003 William Allen Simpson <wsimpson@greendragon.com>
+Copyright 2000 Niels Provos <provos@citi.umich.edu>
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+1. Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in the
+   documentation and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+###########################################################################
+
+
+[0] https://www.openssh.com/portable.html
+    https://anongit.mindrot.org/openssh.git
+
+[1] https://anongit.mindrot.org/openssh.git/tree/moduli.c
+
+[2] https://anongit.mindrot.org/openssh.git/tree/LICENCE