More details on errors from command line

[timothyhinrichs]

It'd be great if OPA could give more informative error messages when loading data from files. Below is the current behavior, where there's a problem with the bar.json file. If the error message could include the file that generated the error, that'd be helpful.

$ ./opa_darwin_amd64 run foo.rego bar.json baz.json
invalid character '}' looking for beginning of object key string