Add some missing UT cases (#51)

Add Apple clang to the list of tested compilers.

Merge pull request #46 from Lastique/feature/remove_static_assert

b2 --with-headers

Remove dependencies on Boost.StaticAssert.

Add Boost::Compat to the CMake test dependencies.

Mock timer and resolver in unit tests.

When resending packets, revalidate them with new connack props.

tests: Add missing asio::system_executor include.

Correct StreamType concept in the docs.

Add AppleClang to CI.

Reconnect on all transport layer errors and log them.

Drop Spirit dependency

Fix CI by targeting win10 winapi

Fix for c++17