Add new packages and build scripts for various libraries

- Added Nuklear GUI library with build script and configuration.
- Introduced OpenH264 encoder/decoder with build configuration.
- Added PortAudio library for audio I/O with custom build script.
- Included Python Execnet for multi-Python deployment.
- Added Pytest Xdist plugin for distributed testing.
- Introduced Shaderc for shader compilation tools.
- Added Snappy compression library with necessary patches and configuration.
- Included SoundTouch audio processing library with build configuration.
- Added SRT library for secure reliable transport.
- Introduced VapourSynth video processing framework with configuration.
- Added Vid.stab for video stabilization.
- Included WebRTC Audio Processing library with build configuration.
- Added X264 video encoding library with patches for POSIX compliance.
- Introduced X265 video encoder with build configuration.
- Added XKeyboard Config for X keyboard configuration files.
- Included Xorg XKBComp for keyboard description compilation.
- Added Xvidcore MPEG-4 video codec library with configuration.
- Introduced ZeroMQ messaging system with patches and build configuration.
- Added Zimg library for scaling and colorspace conversion.

extra/libpaper/localepaper.c

@@ -0,0 +1,44 @@
+/*
+ * localepaper: print the dimensions in mm of the current locale's
+ * paper size, if possible.
+ *
+ * Based on a patch by Caolan McNamara:
+ * http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=481213
+ *
+ * Copyright (C) Reuben Thomas <rrt@sc3d.org>, 2013.
+ *
+ * Copying and distribution of this file, with or without modification,
+ * are permitted in any medium without royalty provided the copyright
+ * notice and this notice are preserved.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <locale.h>
+#if defined LC_PAPER && defined _GNU_SOURCE
+#include <langinfo.h>
+#endif
+
+#include "progname.h"
+
+int main(int argc, char *argv[])
+{
+  set_program_name(argv[0]);
+  argc = argc; /* Avoid a compiler warning. */
+
+#if defined LC_PAPER && defined _GNU_SOURCE
+  setlocale(LC_ALL, "");
+
+#define NL_PAPER_GET(x) \
+  ((union { char *string; unsigned word; })nl_langinfo(x)).word
+
+  printf("%d %d\n", NL_PAPER_GET(_NL_PAPER_WIDTH), NL_PAPER_GET(_NL_PAPER_HEIGHT));
+  return EXIT_SUCCESS;
+
+#else
+  printf("%s: locale paper size information is not supported on this system", program_name);
+  return EXIT_FAILURE;
+#endif
+}