fix#1435, fix#1438
* Example and test can be built on msvc v141 15.9.6
using /std:c++17 and BOOST_BEAST_USE_STD_STRING_VIEW.
* changed string_view.to_string() to std:string(string_view),
awaiting availability of Library Fundamentals TS here.
* Reactivated relevant tests to param_list. #ifdef 0 test
exhibited same assertion failed error in debug mode.
Now fixed in DEBUG on msvc v141 15.9.6 with
BOOST_BEAST_USE_STD_STRING_VIEW and /std:c++17.
* Looked up http paramters (transfer-encoding, etc.)
and changed tests as well as fixing comment to
match specs.
