Implemeted put/get key-value pairs:.

PUT /addkey/$key_id$
body: value
Response: 200 OK

GET /getkey/$key_id$
Response 200 OK
body: value

* Wrapped CPP polymorphic behavior in Cython
* CMake improved
* Still not using C++11, because boost::properties, which we use to
  read json, generates a compilation error