Enhancements

• Add the Jason.OrderedObject struct
• Support decoding objects preserving all the keys with objects: :ordered_objects option
• Support decoding floats to Decimal with floats: :decimals option
• Add ~j and ~J sigils in module Jason.Sigil to support writing JSON literals in code

Fixes

• Fix error reporting when decoding strings (it was possible to mis-attribute the offending byte)
• Verify fields given to @derive