Previously the timestamp_formats field in the response
from the find_file_structure endpoint contained Joda
timestamp formats. This change makes that clear by
renaming the field to joda_timestamp_formats, and also
adds a java_timestamp_formats field containing the
equivalent Java time format strings.
Previously numeric values in the field_stats created by the
find_file_structure endpoint were always output with a
decimal point. This looked unfriendly and unnatural for
fields that clearly store integer values. This change
converts integer values to type Integer before output in
the file structure field stats.