mappings/VegCSV-VegBIEN.specimens.csv: eventDate mappings: Removed collectiondate mapping because the eventDate refers only to the plot event. Added /_alt suffixes for mergability with DwC.

mappings/DwC2-VegBIEN.specimens.csv, DwC1-DwC2.specimens.csv: Split eventDate into eventDate and dateCollected, where eventDate refers only to the date of the sampling event, but dateCollected also refers to the date the particular specimen was collected. (This distinction is important in merging with VegCSV, because in plots data, these two fields are distinct.) Remapped datasources with dateCollected-related fields to new dateCollected.

bin/map: Run new xml_func.simplify() on the root before printing the put template, so that _alts and _merges with only one element for the current datasource will be printed in their simplified form (with the _alt/_merge removed). This faciliates automated testing after an _alt/_merge suffix has been added, because the put template provided as part of the automated test will only change for those datasources that actually have an entry for both mappings, which greatly reduces the number of tests that need to be accepted.

xml_func.py: Added simplify()

xpath.py: put_obj(): Use new get_values(), so that the returned nodes are not modified by XML tree transformations, such as those performed by xml_func.process()

Added get_values()

xml_dom.py: is_empty(): Treat whitespace-only text nodes (including text nodes containing empty strings) as empty. This will also support None equivalents in text nodes, because they are isspace_none_str, which is considered whitespace.

xml_func.py: _map(): Don't remove None params, because are valid values and must be supported. This will become an issue once empty strings in text nodes are considered equivalent to None.

xml_func.py: _units(): Don't remove None params, because are valid values and must be supported. This will become an issue once empty strings in text nodes are considered equivalent to None.

xml_func.py: _name(): Fixed bug where needed to pass None values through and handle no name parts to properly support NULL propagation