sql_gen.py: Added to_name_only_col()

sql_gen.py: Added as_Value()

sql.py: mk_select(): conds: Use new sql_gen.ColValueCond instead of sql_gen.as_ValueCond(). Documented that Code and ValueCond are sql_gen objects.

sql_gen.py: Added ColValueCond

sql.py: mk_flatten_mapping(): Filter str(col) through clean_name() to remove quotes, etc.

sql.py: Added clean_name()

sql.py: put_table(): Join together input tables into new table for speed and so don't modify input if values edited

sql.py: mk_flatten_mapping(): Take as_items param to return a list of dict items instead of a dict. Sort preserve cols before other cols. flatten(): Turn on as_items so that cols list is sorted in input order, with preserve cols first. This ensures that if a pkey is provided in preserve, it will be the first col in the generated table.

sql.py: mk_flatten_mapping(), flatten(): Take list of cols to select instead of using all cols in all tables to join

sql.py: mk_flatten_mapping(), flatten(): Renamed flat_table param to into to be consistent with run_query_into() and put it first because it is the output param