coud not support the asynchronous non-blocking send? curl_multi_perform #183

Expected behaviour

Actual behaviour

Environment and debugging details

• compiler and version
• operating system
• version of restclient-cpp
• how did you install restclient-cpp? (via packages, git, tarball)
• libcurl version and compile flags
• full error output of your build as an inline codeblock or gist

(some of these things might not apply but the more you can provide the easier
it will be to fix this bug. Thanks!)