#145 add a removeItem method to collection classes.

[Rick McGuire]

The collection classes could really use a removeItem method. Among other uses, it could really improve the algorithms of the set methods.

[Rick McGuire]

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This also made the second argument on the relation removeitem() method optional.

[Rick McGuire]

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This added removeItem(item) to all collection classes. This will remove an item from the collection. The return value is the item removed. If an item exists under more than one index, the item removed is unspecified.

Note: This also made the index argument to the RELATION removeItem() method optional.