Add Conan packaging

[mmha]

This changes the following things:

1. Tests and examples now build optionally. To build them, pass -DBUILD_TESTS=1 or -DBUILD_EXAMPLES=1 to CMake respectively
2. Added a conanfile.py that retrieves the git commit hash, sets it as the package version and packages cmcstl2 up along with the CMake package. A disadvantage is that there can be no version ranges and forces downstream users to specify the commit they want, but given the instability of the API this is probably fine.
3. Modified the .travis.yml such that it automatically packages up cmcstl2 after running the tests and uploads it to Bintray. For this to work you need to create your own Bintray account, and set some environment variables just like in this example. Look at my source branch to see it all in action.
4. Document it all for the user in the README.md

Please note that I inserted my own Bintray badge into the README. You need to change it to your own after you created your own Bintray account.