$schema KEYWORD not present in the schema generated

[tikaa]

Hello,

according to 6.1 bullet in [1] the $schema keyword is recommended to be included in the json schema as a root element. I could not observe this element in the json schema generated by this tool.

[1] http://json-schema.org/latest/json-schema-core.html#anchor22

[highsource]

Should be no big deal to add this. Feel free to send me a pull request, I don't know when I'd come to this myself.