refextract: new unit test suite

• Unit test suite for refextract. Includes a test for comprehensive list of example reference lines, directly from the 'test_reference_lines' list from refextract (~50 reference lines, generating ~100 split citations). Embodying author recognition as well as DOI, URL, journal titles, report numbers and multiple cites within a single reference line. This version happens to rely on the CDS-specific representation of journal titles, in the format: %(title)s %(volume)s (%(year)s) %(page)s as opposed to the format for INSPIRE: %(title)s, %(volume)s, %(page)s, %(year)s