bin/map: Documented that it is duplicate-column safe (supports multiple columns of the same name)

README.TXT: Datasource setup: Obtaining CSVs: Documented that when exporting relational databases to CSVs, you MUST ensure that embedded quotes are escaped by doubling them, not by preceding them with a "\" as is the default in phpMyAdmin

csvs.py: delims: Added ";", which is phpMyAdmin's default CSV delimiter

sql_io.py: null_strs: Added 'NULL', which is used by phpMyAdmin as the default "Replace NULL with" value for CSV exports

sql_io.py: cleanup_table(): Refactored to use for loop with array constant, so that additional NULL-equivalent strings can easily be added

mappings/roots/: Merged roots for different tables into one mappings/root.sh for Veg+, which handles all tables' mappings to VegBIEN

sql_io.py: put_table(): When ignoring all rows for an iteration, return literal NULL value instead of column of NULLs as an optimization for callers using that iteration's pkeys

inputs/import.stats.xls: Updated with stats from latest import

mappings/VegCore-VegBIEN.csv: Primary taxondetermination: Removed [role=identifier] because the role of the entity making the determination is unknown. Added [!isoriginal] filter to those mappings to ensure that primary taxondetermination XPaths map to a different taxondetermination than the [isoriginal=true] determination when both are present.

inputs/SALVIAS*/1.organisms/map.csv: Remapped cfaff to identificationQualifier, because it was previously mapped to the same taxondetermination as the Orig* terms but does not have a corresponding Orig prefix to indicate that it should apply to the original determination instead of the primary TNRS one