v0.5.2

• Fixed: PostgreSQL: Issue #14 (Error when trying to save a record into a table if partitioned column value had special characters inside, using string_firstchars and string_lastchars partition subtypes)
• Fixed: PostgreSQL: Issue #11 (Error when trying to save a record into a table that was partitioned by a column that can be NULL, now if a column, that was used for partitioning, has NULL value it will be inserted into a special partition with _null postfix)
• Fixed: SQLObject: Error when trying to partition a model with a field that has a default attribute set to some value