Merge remote-tracking branch 'upstream/master' into voip

CMakeLists.txt

appveyor.yml

include/mtx/events.hpp

include/mtx/events/collections.hpp

include/mtx/events/presence.hpp

include/mtx/responses/sync.hpp

include/mtxclient/http/client.hpp

include/mtxclient/http/session.hpp

lib/http/client.cpp

lib/structs/events.cpp

lib/structs/events/collections.cpp

lib/structs/events/presence.cpp

lib/structs/responses/common.cpp

lib/structs/responses/sync.cpp

lib/utils.cpp

tests/client_api.cpp

tests/events.cpp