Created 3Party, added gtest and cereal.

Hi Alex @deathbaba,

Creating ```3Party```. Please take a look at:

1. Licenses and the directory structure. I did my best to follow what we have discussed.
2. The way I added gtest (original code https://github.com/dkorolev/3Party/commit/ce2baa9420ce74191da9911622c3e058d563ac56, followed by my port https://github.com/dkorolev/3Party/commit/95ddb4b2770f998a17456a60df05376b838f9b13).
3. Whether it builds and runs on Mac.

Here's how it looks to me now:

```
dima@dima-i9:~/github/dkorolev/3Party/example/gtest$ make
mkdir -p build
g++ -std=c++11 -Wall -o build/demo demo.cc -pthread
./build/demo
[==========] Running 6 tests from 3 test cases.
[----------] Global test environment set-up.
[----------] 4 tests from GTestTest
[ RUN      ] GTestTest.Trivial
[       OK ] GTestTest.Trivial (0 ms)
[ RUN      ] GTestTest.Passing
[       OK ] GTestTest.Passing (0 ms)
[ RUN      ] GTestTest.DeathTest
[       OK ] GTestTest.DeathTest (2 ms)
[ RUN      ] GTestTest.ExceptionThrowingTest
[       OK ] GTestTest.ExceptionThrowingTest (0 ms)
[----------] 4 tests from GTestTest (3 ms total)

[----------] 1 test from GTestTemplatedTest/0, where TypeParam = std::vector<int, std::allocator<int> >
[ RUN      ] GTestTemplatedTest/0.TemplatedContainersTest
[       OK ] GTestTemplatedTest/0.TemplatedContainersTest (0 ms)
[----------] 1 test from GTestTemplatedTest/0 (0 ms total)

[----------] 1 test from GTestTemplatedTest/1, where TypeParam = std::deque<int, std::allocator<int> >
[ RUN      ] GTestTemplatedTest/1.TemplatedContainersTest
[       OK ] GTestTemplatedTest/1.TemplatedContainersTest (0 ms)
[----------] 1 test from GTestTemplatedTest/1 (0 ms total)

[----------] Global test environment tear-down
[==========] 6 tests from 3 test cases ran. (3 ms total)
[  PASSED  ] 6 tests.

  YOU HAVE 1 DISABLED TEST

dima@dima-i9:~/github/dkorolev/3Party/example/gtest$ 
```

Thanks,
Dima