Added inputs/REMIB

bin/map: Deal with fields that may be in the dataset under more than one prefix by getting all fields and coalesce()ing them (e.g. SpeciesLink has dwcore* and darwin1* columns for the same DwC field)

util.py: Added coalesce()

xpath_func.py: process(): Fixed bug where XPath elem's other_branches were not also processed

row: Don't prepend header row because this feature prevents the program from being used on a pipeline. Sheets may be constructed in a pipeline if multiple segments need to be joined, e.g. with cat_csv.

Added row to get a row of a spreadsheet, preceded by the header row

bin programs: Fixed bug in Usage message where program name was not printed because unset variable $self was used instead of $0

xml_func.py: _nullIf: types_by_name: Use strings.ustr instead of str to support Unicode values

xml_func.py: _nullIf: If value not convertible, return it, because can't equal null. Refactored to store types by name in a dict instead of using if statements.

units.py: convert(): raise MissingUnitsException if quantity doesn't have units. MissingUnitsException: Take Quantity input instead of str.