v2.1

Important: security fix for Client: added host verification

Other improvements:

• Added threaded heavy work example
• Added io_test and CI
• Added install target
• Replaced class visibility private with protected
• Force TLS 1.2
• Added exception handler to handle exception throws in Server
• Less copies of shared_ptr objects
• Possibility to set or reuse boost::asio_ioservice
• Use of std::regex with clang and g++ if possible
• Improvement of default_resource example
• Timeout can be set on client requests
• Various MSVS fixes
• Added proxy server support to Client
• Various minor bug fixes.