Add support for external boost and asio library usages. (#490)
Add support for external boost and asio library usages. (#490)

fixes https://github.com/hazelcast/hazelcast-cpp-client/issues/474
hazelcast/hazelcast-cpp-client,hazelcast/hazelcast-cpp-client,hazelcast/hazelcast-cpp-client,hazelcast/hazelcast-cpp-client