This commit adds the flag --only-if-modifying to
the dtc subcommand `post-records`. If `--curate`
is provided, it will check whether an identical
record already exists in the curated area of the
collection, and ---if the record already exists---
refuse to overwrite it.
Record matching can be "relaxed" by exluding
elements from the matching process. This can be
done using the option `--ignore-spec`.
This commit adds the class RecordComparer. Instances
of this class can compare dictionaries, while
ignoring certain elements.
This can be useful, for example, to determine if
two records are equal, except for the content of
the key 'annotations'.
