Update //third_party/protobuf to version 3.

third_party/protobuf/README.md

Index: third_party/protobuf/README.md
diff --git a/third_party/protobuf/README.txt b/third_party/protobuf/README.md
similarity index 70%
rename from third_party/protobuf/README.txt
rename to third_party/protobuf/README.md
index 17551a5a0cbf03ab0cd6583eefe85cc9a667d237..a974d30185f5249658711306c1f96c54c59b349a 100644
--- a/third_party/protobuf/README.txt
+++ b/third_party/protobuf/README.md
@@ -1,17 +1,34 @@
 Protocol Buffers - Google's data interchange format
+===================================================
+
+[![Build Status](https://travis-ci.org/google/protobuf.svg?branch=master)](https://travis-ci.org/google/protobuf) [![Build status](https://ci.appveyor.com/api/projects/status/73ctee6ua4w2ruin?svg=true)](https://ci.appveyor.com/project/protobuf/protobuf)
+
 Copyright 2008 Google Inc.
-http://code.google.com/apis/protocolbuffers/
+
+https://developers.google.com/protocol-buffers/
 
 C++ Installation - Unix
-=======================
+-----------------------
+
+If you get the source from github, you need to generate the configure script
+first:
+
+    $ ./autogen.sh
+
+This will download gmock source (which is used for C++ Protocol Buffer
+unit-tests) to the current directory and run automake, autoconf, etc.
+to generate the configure script and various template makefiles.
+
+You can skip this step if you are using a release package (which already
+contains gmock and the configure script).
 
 To build and install the C++ Protocol Buffer runtime and the Protocol
 Buffer compiler (protoc) execute the following:
 
-  $ ./configure
-  $ make
-  $ make check
-  $ make install
+    $ ./configure
+    $ make
+    $ make check
+    $ make install
 
 If "make check" fails, you can still install, but it is likely that
 some features of this library will not work correctly on your system.
@@ -21,7 +38,7 @@ Proceed at your own risk.
 
 For advanced usage information on configure and make, see INSTALL.txt.
 
-** Hint on install location **
+**Hint on install location**
 
   By default, the package will be installed to /usr/local.  However,
   on many platforms, /usr/local/lib is not part of LD_LIBRARY_PATH.
@@ -33,7 +50,7 @@ For advanced usage information on configure and make, see INSTALL.txt.
   If you already built the package with a different prefix, make sure
   to run "make clean" before building again.
 
-** Compiling dependent packages **
+**Compiling dependent packages**
 
   To compile a package that uses Protocol Buffers, you need to pass
   various flags to your compiler and linker.  As of version 2.2.0,
@@ -71,7 +88,23 @@ For advanced usage information on configure and make, see INSTALL.txt.
   If you only want protobuf-lite, substitute "protobuf-lite" in place
   of "protobuf" in these examples.
 
-** Note for cross-compiling **
+**Note for Mac users**
+
+  For a Mac system, Unix tools are not available by default. You will first need
+  to install Xcode from the Mac AppStore and then run the following command from
+  a terminal:
+
+    $ sudo xcode-select --install
+
+  To install Unix tools, you can install "port" following the instructions at
+  https://www.macports.org . This will reside in /opt/local/bin/port for most
+  Mac installations.
+
+    $ sudo /opt/local/bin/port install autoconf automake libtool
+
+  Then follow the Unix instructions above.
+
+**Note for cross-compiling**
 
   The makefiles normally invoke the protoc executable that they just
   built in order to build tests.  When cross-compiling, the protoc
@@ -94,7 +127,7 @@ For advanced usage information on configure and make, see INSTALL.txt.
   has the same version as the protobuf source code you are trying to
   use it with.
 
-** Note for Solaris users **
+**Note for Solaris users**
 
   Solaris 10 x86 has a bug that will make linking fail, complaining
   about libstdc++.la being invalid.  We have included a work-around
@@ -104,7 +137,7 @@ For advanced usage information on configure and make, see INSTALL.txt.
 
   See src/solaris/libstdc++.la for more info on this bug.
 
-** Note for HP C++ Tru64 users **
+**Note for HP C++ Tru64 users**
 
   To compile invoke configure as follows:
 
@@ -112,16 +145,24 @@ For advanced usage information on configure and make, see INSTALL.txt.
 
   Also, you will need to use gmake instead of make.
 
+**Note for AIX users**
+
+  Compile using the IBM xlC C++ compiler as follows:
+
+    ./configure CXX=xlC
+
+  Also, you will need to use GNU `make` (`gmake`) instead of AIX `make`.
+
 C++ Installation - Windows
-==========================
+--------------------------
 
-If you are using Microsoft Visual C++, see vsprojects/readme.txt.
+If you are using Microsoft Visual C++, see cmake/README.md.
 
 If you are using Cygwin or MinGW, follow the Unix installation
 instructions, above.
 
 Binary Compatibility Warning
-============================
+----------------------------
 
 Due to the nature of C++, it is unlikely that any two versions of the
 Protocol Buffers C++ runtime libraries will have compatible ABIs.
@@ -132,10 +173,10 @@ immediately on startup of your app.  Still, you may want to consider
 using static linkage.  You can configure this package to install
 static libraries only using:
 
-  ./configure --disable-shared
+    ./configure --disable-shared
 
 Java and Python Installation
-============================
+----------------------------
 
 The Java and Python runtime libraries for Protocol Buffers are located
 in the java and python directories.  See the README file in each
@@ -144,9 +185,9 @@ Note that both of them require you to first install the Protocol
 Buffer compiler (protoc), which is part of the C++ package.
 
 Usage
-=====
+-----
 
 The complete documentation for Protocol Buffers is available via the
 web at:
 
-  http://code.google.com/apis/protocolbuffers/
+    https://developers.google.com/protocol-buffers/