allow nested refs on urls and filepaths

[BelfordZ]

the code on this line:
https://github.com/json-schema-tools/reference-resolver/blob/master/src/reference-resolver.ts#L140
and this line
https://github.com/json-schema-tools/reference-resolver/blob/master/src/reference-resolver.ts#L154

need to check the hash fragment of the url/file path and resolve nested refs as we do here:
https://github.com/json-schema-tools/reference-resolver/blob/master/src/reference-resolver.ts#L132