Brain

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* added mechanisms for creating/opening the database
* hid ID creation inside database class and made ModifyRequest return ID of the created object
* moved request tests to a higher level, so that they can be used for DBs written using different languages
* created user-friendly API for requests and connections
* added support for processing several requests inside a single transaction
* moved to Python 3.1

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* added support for int, float, binary and null types along with corresponding search conditions.
* logic and structure layers separated almost completely

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* greatly refactored database layer; structure and logic are still kind of tangled though
* fixed some flaws in database logic, added unittests for these cases
* each request is transacted now
* added protection from SQL injection (hid it in db engine-specific class)
* added exceptions to requests

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* test_database.py is split, separate module for each request is created
* some unit-tests added
* added request format checks to interface classes
* added unit-tests for interface format checks

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Added support for insertion and deletion requests in nested lists.

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Added nested lists support without insert and delete requests (positions in list
should be specified explicitly).