Feature / Fix: Add Content-Length: 0 request header for empty POST request etc. (#120 by @clue)

Fix: Only try to follow redirects if Location response header is present. (#130 by @clue)

Documentation and example for SSH proxy (SSH tunnel) and update SOCKS proxy example. (#116, #119 and #121 by @clue)

Improve test suite and also run tests on PHP 7.3. (#122 by @samnela)