Added format_sql, format_sql_to and basic_format_context
Boost.Charconv is now a mandatory dependency
Text queries are now locale-independent
any_connection::current_character_set now uses system::result
Added any_connection::format_opts
field_view, field and statement::bind now disallow character types
escape_string can now be used with any OutputString type
Added constant_string_view
character_set now uses string_view and span
set_character_set hardening
close#69close#208