craft-xls carried its own CellRef, Range, Value, CellError, Visibility, sheet-name
quoting, built-in number format table and indexed palette. craft-xlsx and craft-ods
need the same ones, so they move to a crate with no dependencies and craft-xls
re-exports them: an application gets one Value and one CellRef whichever file it read.
Added on the way: A1 parsing (CellRef::parse, Range::parse), Range::count and a1,
CellError::parse and the newer error values SpreadsheetML stores as text,
builtin_format_id for writers.
