add initial CMake and Visual Studio build support

This moves the compatibility include files from include to
include/compat so we can use the awful MS C compiler
<../include/> trick to emulate the GNU #include_next extension.

This also removes a few old compat files we do not need anymore.

patches/arc4random.c.patch

@@ -0,0 +1,15 @@
+--- crypto/compat/arc4random.c.orig	2015-07-20 07:41:17.000000000 -0600
++++ crypto/compat/arc4random.c	2015-07-20 07:41:58.000000000 -0600
+@@ -36,8 +36,11 @@
+ #define KEYSTREAM_ONLY
+ #include "chacha_private.h"
+ 
++#ifndef min
+ #define min(a, b) ((a) < (b) ? (a) : (b))
+-#ifdef __GNUC__
++#endif
++
++#if defined(__GNUC__) || defined(_MSC_VER)
+ #define inline __inline
+ #else				/* !__GNUC__ */
+ #define inline