new tools, rdm2eprint, ep3util

This release is focused on adding two new tools to back port our RDM content to our feeds system. ep3util mirrors rdmutil in irdmtools. It uses the same command structure but is limited to read only functionality. rdm2eprint will read a RDM record via RDM's JSON API and return an EPrint compatible structure for metadata (i.e. excludes support for .documents and .documents.files). It can be sued to process lists of RDM ids or individual rdm ids. It can support rendering as EPrint XML for comparison and debugging purposes. It includes a harvest option which retrieve records from RDM, convert to an EPrint JSON sturcture then save them in a dataset collection.

Also fixed a JSON encoding/decoding bug by using custom JSON encoders/decoders across irdmtools.