affiliation data collection

[yryo617]

start of affiliation data collection.
tools/affiliations.py contains:

• class to store dated affiliation entries
• class to store list of identifiers and list of dated affiliation entries
• function to add sorts the entries
• function to consolidate the consecutive affiliation entries

examples/identifier_affiliation_mappings_rfc.py contains:

• example code showing how affilliations.py can be used to collect all the affiliation entries going through authors data in rfc

tests/test_tools_affiliations.py contains:

• very simple rudimentary tests of some of the functions in affiliations.py