Deduplicate list of fields per author in AuthorSearch()

[Michael-E-Rose]

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Apparently it can happen that an author has duplicated publication counts by field.

For instance, the result of AuthorSearch('authlast(selten) and authfirst(reinhard)') (our test case) has:

[{'@abbrev': 'ECON', '@frequency': '51', '$': 'Economics, Econometrics and Finance (all)'},
 {'@abbrev': 'ECON', '@frequency': '21', '$': 'Economics, Econometrics and Finance (all)'},
 {'@abbrev': 'BUSI', '@frequency': '8', '$': 'Business, Management and Accounting (all)'}]

We should deduplicate this and sum same entries. So that the result of:

s1 = AuthorSearch('authlast(selten) and authfirst(reinhard)', refresh=30)
print(s1.authors[0].areas)

is ECON (72); BUSI (8).