Merge pull request #28 from kevin--/support-cpp20

std::result_of is removed in C++20 in favor of std::invoke_result

Merge pull request #27 from kevin--/remove-extra-semi

remove extraneous semi colon to suppress -Wextra-semi

version 0.4.0

version 0.3.4

version 0.3.3

version 0.3.2