Added writer.
Added first script (normalise/identity transform).
Updated to use as function as well as command-line script.
Added hxl.parser.tags property function (to be simplified).
Added property functions hxl.model.HXLRow.data and hxl.parser.HXLReader.headers
Removed hxl.writer -- not needed.

Changed hxl.scripts.normalize to use regular CSV writer.
Changed tests to Spanish, to give UTF-8 a proper workout.
More Spanish fields, and rearranged sample-data order to be more natural.
Added tests for language codes.
Use __slots__ in model classes to reduce memory consumption (and
detect attribute mistakes).
Added hxl.model.column.columnNumber and
hxl.model.column.sourceColumnNumber.

Next: eliminate hxl.model.value.columnNumber and hxl.model.value.sourceColumnNumber.
Eliminated hxl.model.HXLValue.columnNumber and
hxl.model.HXLValue.sourceColumnNumber (use values in hxl.model.HXLColumn).
Simplified model that creates HXLValue objects only on demand.
Fixed to use new HXLRow.values
Added hxl.parser.HXLParseException
Added docstring.
Added HXLValue.get and HXLValue.getAll for easy dictionary-style lookup.
Added command-line script to count distinct values for a HXL tag.
Document scripts.
Fixed Markdown