Add support for retrieving HTTP version of a request in HTTP listener

[garethsb]

This PR follows on from #507 by providing a mechanism to allow the HTTP version of the incoming message to be retrieved in the HTTP listener. (One motivation is to allow construction of access logs in Common Log Format.) A basic unit test is included.

It also changes http_request::get_remote_address() introduced by #507 to http_request::remote_address() for consistency with pre-existing member functions of this class.

It also includes a commit that fixes #545 which has been reported against #507.

[msftclas]

All CLA requirements met.

[ras0219-msft]

Thanks!

I changed http_version to be a full struct instead of just using a pair, for bonus type safety. I also restored the older get_remote_address() to avoid breaking source compatibility (with a deprecation warning).

[garethsb]

Thanks for working on these, @ras0219-msft. I think there is one problem with the struct http_version commit. operator>> with uint8_t doesn't do what we want, it reads a character. If I'm right, we need to restore the temporary unsigned ints, around here: 1d35847#diff-d8600089329e519f56170a2d16d7102cR657.

[ras0219-msft]

You are absolutely right. I'll address this tomorrow or I'd be happy to merge a PR.

[garethsb]

Perhaps it's worth pulling the parsing code out into a unit testable function?
E.g. add from_string() and to_string() to http_version?
(Or op>> and op<<?)

[garethsb]

Ah, the existing unit test is failing when cpprestsdk is configured with CPPREST_HTTP_LISTENER_IMPL as asio, so that's something!

...\tests\functional\http\listener\request_handler_tests.cpp(466): error : Failure in http_version:
CHECK_EQUAL(true, httpVersion == http_versions::HTTP_1_1) where true=1 and httpVersion == http_versions::HTTP_1_1=0