Support required, minOccurs, maxOccurs

[highsource]

See:

• Generate "required" : [...] for XSD use="required"  jsonix-schema-compiler#50
• Generate minOccurs/maxOccurs in JSON Schema jsonix-schema-compiler#40
• Include multiplicity in mapping files jsonix-schema-compiler#23
• Generate JS-mapping with minOccurs/maxOccurs jsonix-schema-compiler#33