Parses claims.yml and validates it. Each claim must have a non-blank id,
claim, criterion, measured, status and tier. status must be
pass, fail, open or undeclared; tier an integer from 0 to 3; and
parasite, if given, falciparum or vivax. Ids must be unique, and an
undeclared claim must have NONE DECLARED in its criterion. A violation,
or an empty register, is an error.
Usage
read_claims(path = find_claims())