IOCP and Darwin fixes

The Happy Eyeballs test should no longer intermittently fail on windows

Happy Eyeballs in event loop

Also now enforcing the contract that client_bootstrap setup_callback is always called exactly once, and if it is called with a non-zero error_code, the shutdown_callback will NOT be called.

Test harness fixes

move TLS test from aws-c-http -> aws-c-io (#141)

* move TLS test from aws-c-http to aws-c-io
* minor touchups to tls/socket shutdown logic

Updates needed for aws-c-http testing

v0.3.9

testing_channel_install_downstream_handler() (#137)

Added backtraces to asserts

assert() -> AWS_ASSERT(), removed assert.h includes (#134)

* assert() -> AWS_ASSERT(), removed assert.h includes

* added assert.h to clang-tidy restrictions

PKI buffers are now guaranteed to be null terminated.

v0.3.7

Fixed dll symbol export, made sure PKI buffers were always null termi…

input streams and testing_channel changes

v0.3.6

testing_channel_drain_queued_tasks (#130)

Happy eyeballs error reporting fixes

pass err_code along to setup_callback (#129)

* pass err_code along to setup_callback

* Ensure there is always an error code when happy eyeballs fails

Host resolver lifetime fix

v0.3.4

Copy host_resolution_config into host_entry to prevent lifetime issue…

TLS negotiation timeout fix

v0.3.3

Ensure that setup_callback is always called at least once when using …