Support $raw
Support $include
Support 'number' type
Support $defs in array item
Update Readme
Support cascading $def
Support global $def defined by `$_`
Fix: cannot find relative path
Fix: $include does not expend to valid jsonschema
Tune error
Fix: crash when use nonexist type
Fix: cannot parse $include relative path multiple times in runtime
Bump to 0.2.0