v0.3.0

• BREAKING asyncgi::Router now depends on asyncgi::IO:

auto io = asyncgi::IO{};
auto router = asyncgi::Router{io};

• BREAKING ErrorHandler was replaced with EventHandlerProxy - a flexible callback system allowing backwards-compatible extension.
  Currently only error event handlers are supported with the signature void(asyncgi::ErrorEvent, std::string_view);
  Event handler is passed as the last parameter to the asyncgi::IO object's constructor:

auto io = asyncgi::IO{[](asyncgi::ErrorEvent, std::string_view errorMsg){ std::cerr << errorMsg << "\n";}};

It's planned to add an optional logger based on this system in the future releases. The event handling will be documented then.