v0.6.0

• Check that InputIt is an iterator to enable the insert functions with iterators. This prevents some potential overload conflicts between insert functions.
• We now use std::hash<std::basic_string_view<CharT>> as default hash function instead of FNV-1a if std::string_view is detected.
• Add support for efficient serialization (#19)
• Fix compilation error with GCC 9, the implicit copy/move constructor/operator of the iterator were not generated.