add unit test for async-response
fix start_test_server script
do not shutdown server when "Too many open files in system"
host is mandatory in http/1.1; do not open connection too fast, netty accept a little slow
code to make idle http connection to test how server behave with concurrent connection
add zh documentation
fix link
Use `reduce-kv` for client `transform-header` fn (faster)
Rename `keyify?` -> `keywordize?`
Superficial client code tweaks