Littletable

(renamed project from dulce to littletable)
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- Improved exception message when duplicate or None value is given for a
unique index attribute.

- Support for namedtuples and __slots__-defining objects supplied by Colin
McPhail, thanks!

- Added Table.pivot() method, to return a pivot table on one or more
attributes. New PivotTable class includes methods for extracting data in
both Table and tabular formats.

- Added more details to the docstring for Table.join, to more completely
describe the sequence of steps to join 2 or more Tables, using join(), or
join_to and '+'. Also, removed table_name argument in Table.join, to
simplify this call (the resulting table can be easily renamed using Table
call form).

- Python 3 compatibility changes, importing simplejson or json, as
appropriate - thanks again to Colin for the Python compatibility testing.

- Renamed _TableJoin to JoinTerm, and added documentation on how it is used
to build up table joins using '+' addition notation.

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- Fixed typo in module docstring, "wishlists" should be "wishitems" (as shown
correctly in dulce_demo.py). Also fixed typo in docs for Table.create_index,
caused by my lack of epydoc-fu. Plus some general cleanup of the
docstrings. Thanks, Colin McPhail for reporting these!

- Changed _orderby and _orderbydesc flags to just _orderby, taking a single
string containing a comma-separated list of attribute names (this is
necessary since **kwargs does not preserve arguments order).

- Changed Table attribute "name" to "table_name", so as not to collide with
a user-defined index on an attribute named "name".

- Added support for unique indexes to allow or disallow null key values. If
null keys are allowed, then all records with a null key are stored in an
internal list.

- Added some join performance pickup, using the table with the smaller number
of keys as the outer loop in finding matching records.

- Added query performance pickup, when using multiple indexed attributes in
query.

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Initial prototype release