Adding third-party submodules.
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..0929c8e
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,15 @@
+[submodule "third_party/zlib"]
+ path = third_party/zlib
+ url = https://github.com/madler/zlib
+[submodule "third_party/openssl"]
+ path = third_party/openssl
+ url = https://github.com/openssl/openssl.git
+ branch = OpenSSL_1_0_2-stable
+[submodule "third_party/protobuf"]
+ path = third_party/protobuf
+ url = https://github.com/google/protobuf.git
+ branch = v3.0.0-alpha-1
+[submodule "third_party/libevent"]
+ path = third_party/libevent
+ url = https://github.com/libevent/libevent.git
+ branch = patches-2.0