* Optimize hash calculation and equality for field strings
Experiments show the digest and equality functions taking the
most time. Optimizing L1 cache usage did not show significant
improvements.
fix#1133, fix#1241
When the macro BOOST_BEAST_USE_STD_STRING_VIEW is defined,
Beast will use std::string_view instead of boost::string_view.
The name boost::beast::string_view is a type alias for the
chosen view type.
