Added .gitattributes to exclude certain directories from git-archive

.gitattributes

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+/examples export-ignore
+/ports export-ignore
+/test export-ignore
+.gitattributes export-ignore
+.gitignore export-ignore

ports/Homebrew/README.md

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+Homebrew formula for libzt/libztcore
+======
+
+This formula script is only here for archival purposes. To install `libzt` and `libztcore` via Homebrew use:
+
+```
+brew tap zerotier/libzt
+brew install libzt
+```
+
+Once accepted into Homebrew core this will be shortened to:
+
+```
+brew install libzt
+```

ports/Homebrew/libzt.rb

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+class Libzt < Formula
+  desc "ZeroTier: libzt -- An encrypted P2P networking library for applications"
+  homepage "https://www.zerotier.com"
+
+  version "1.3.0"
+
+  stable do
+    url "https://github.com/zerotier/libzt.git", :branch => "master", :revision => "3d1159882117278fcb5fabb623bd62175b6c7e6c"
+  end
+
+  bottle do
+    root_url "https://download.zerotier.com/dist/homebrew"
+    cellar :any
+    sha256 "e1ac8425fd0ea510c7db734af8d6c41cd3650b12f66a571f9d818c0121422eee" => :mojave
+  end
+
+  devel do
+    version "1.3.1"
+    url "https://github.com/zerotier/libzt.git", :branch => "dev"
+  end
+
+  head do
+    url "https://github.com/zerotier/libzt.git"
+  end
+
+  depends_on "cmake" => :build
+  depends_on "make" => :build
+
+  def install
+    system "make", "update"
+    system "cmake", ".", *std_cmake_args
+    system "cmake", "--build", "."
+    system "make", "install"
+    cp "LICENSE.GPL-3", "#{prefix}/LICENSE"
+  end
+
+  def caveats
+    <<~EOS
+      Visit https://my.zerotier.com to create virtual networks and authorize devices.
+      Visit https://www.zerotier.com/manual.shtml to learn more about how ZeroTier works.
+      Visit https://github.com/zerotier/ZeroTierOne/tree/master/controller to learn how to run your own network controller (advanced).
+    EOS
+  end
+
+  test do
+    # Writes a simple test program to test.cpp which calls a library function. The expected output of this
+    # function is -2. This test verifies the following:
+    # - The library was installed correctly
+    # - The library was linked correctly
+    # - Library code executes successfully and sends the proper error code to the test program
+    (testpath/"test.cpp").write <<-EOS
+      #include<cstdlib>\n#include<ZeroTier.h>\nint main(){return zts_socket(0,0,0)!=-2;}
+    EOS
+
+    system ENV.cc, "-v", "test.cpp", "-o", "test", "-L#{lib}/Release", "-lzt"
+    system "./test"
+  end
+end