v0.2.0

Fixes:

• fixed truncation of floating-point values when using ostreams
• fixed missing value deduction guides for dates and times
• fixed potential ODR issues relating to exception mode handling etc.
• fixed some documentation issues

Additions:

• added serialization round-trip tests
• added node::is_number()
• added node_view::is_number()
• added node_view::value_or()
• added hexfloat parsing support for all implementations (not just <charconv> ones)