Release v1.2.0 (#20)

Major Updates

• Added Windows support.
• Added Apple support.
• Added compile-time warnings setup.
• Added DiscardAll and FetchAll in C++.

But Fixes and Other Changes

• Fixed type checking in C++ ConstValue::ValueMap method.
• Fixed pull error handling in the C++ Client::Execute method.
• Fixed various compile-time warnings.
• Fixed mg_session_params_get_client_name by renaming it to mg_session_params_get_user_agent (the one implemented in src/mgclient.c).
• Add advanced C++ example.