fix: change keywords priority for inferring example and try infer example from root in combined schemas

[magicmatatjahu]

PR fixes bugs described in #124 issue. I copied the description of bugs from mentioned issue:

• const should take precedence over other keywords. At the moment package infer examples in order: default -> const -> enum -> examples[0] -> generate example using format, but I think that const should take precedence over other keywords and we should change also whole order, so we should end with priority:
  • const - valid schema should have always value defined in const
  • examples[0] - if we don't have defined const then examples[0] should have next priority
  • enum[0]
  • default - it's a default value for valid schema, but const, examples[0] and enum[0] should have highter priorities - examples and enum in first index can have different value than is defined in default
• if schema has defined examples, default, const with oneOf like in schema above, package should infer examples from root schema, not from first oneOf item -> problem with this line. This problem should be also handled for other combined keywords like allOf.

Changes:

• change the priority of const, examples, default, enum keywords
• try to infer example in combined schemas from root, and only then infer examples from sub schemas
• write tests for changes
• update Readme.md with changed order

[RomanHotsiy]

Great job! 👏

[RomanHotsiy]

Published in v1.1.0