Add BUILD_TESTS option to CMakeLists.txt
Add BUILD_TESTS option to CMakeLists.txt

- OFF by default
- REQUIRES Boost system and filesystem libraries
- When ON builds tiny-cnn/test/test.cpp
- Produces binary called tiny_cnn_test

H4kor/tiny-cnn,zhangqianhui/tiny-cnn,Wangyida/tiny-cnn,Wangyida/tiny-cnn,H4kor/tiny-cnn,zhangqianhui/tiny-cnn