More detailed error messages, error paths

write_full_runkey() and commit_runkey() (located in /example/ and based on HTTP functions post(dic, url, "/stage/create") and post(dic, url, "/stage/commit") often produce bare-bones errors, primarily:

[fully_printed_runkey] is not of type 'object' - 'data'

It would be very nice to have more detail errors here, such as locating where in a runkey the issue occurs (subtree name&path, payload name, etc), and what it's related to (payload issue, data type reference error, format/syntax problem, etc)