Allow for a local poco build
Allow for a local poco build

By default the CMake rules will look for a pre-installed version of
Poco. To build Poco alongside the library invoke cmake as:

    $ cmake -DBUILD_POCO=ON

Signed-off-by: Andrew McDermott <6c6c2766133de5328a68ea38e42dc5bfcce63d27@frobware.com>

deepstreamIO/deepstream.io-client-cpp,deepstreamIO/deepstream.io-client-cpp,deepstreamIO/deepstream.io-client-cpp,deepstreamIO/deepstream.io-client-cpp