Non-standard string_views are super annoying to use

[tgockel]

While setting something like -DUSE_BOOST_STRING_VIEW=1 is easy to make the JSONV library use an alternative string_view implementation, there is no obvious way for consumers of the library (who just use #include and -ljsonv) to pick up the fact that the SO was created using non-default settings until they get a linker error. At the very least, this inconvenience should be documented, but there might be a way to get CMake to do something more clever.