jsonldplayground: load the @context #225

The feature to load independenly the JSON-LD @context , as explained here for the API ,
https://github.com/jsonld-java/jsonld-java#loading-contexts-from-a-string

should be present in the jsonldplayground command line , see my issue :
jsonld-java/jsonld-java-tools#5

According to the output of

jsonldplayground --help

this does not seem to be implemented.