More table references

[trueqbit]

• More "storage" methods and expression factory functions that query mapped objects now accept "table references":
  • These are: iterate(), get_all(), get_all_pointer(), get_all_optional(), count(), get(), get_pointer(), get_optional()
• Provided a table reference for the SQLite master "schema" table.
• Rounded off unit tests.
  • Thorough testing of the callability and the expected results.
• Some methods now accept also table aliases:
  • get_all(): Supported by the statement serializer and when executing a prepared statement from such an expression.
  • iterate(): For completeness.