Feature / Fix: Improve error handling and reporting for happy eyeballs and immediately try next connection when one connection attempt fails. (#230, #231, #232 and #233 by @clue)

Error messages for failed connection attempts now include more details to ease debugging. Additionally, the happy eyeballs algorithm has been improved to avoid having to wait for some timers to expire which significantly improves connection setup times (in particular when IPv6 isn't available).

Improve test suite, minor code cleanup and improve code coverage to 100%. Update to PHPUnit 9 and skip legacy TLS 1.0 / TLS 1.1 tests if disabled by system. Run tests on Windows and simplify Travis CI test matrix for Mac OS X setup and skip all TLS tests on legacy HHVM. (#229, #235, #236 and #238 by @clue and #239 by @SimonFrings)