* The main loader script has been updated to generate the list of files
it needs to load automatically. As a consequence, files that contained
manually-maintained lists of scripts have been removed, and definition
directories have been renamed accordingly.
* PostgreSQL extension loading and configuration has been moved to a
separate script to be loaded automatically in the main transaction.
* Data and function definition scripts that had the -data or -functions
suffix have been renamed (the suffix is unnecessary).
* Unit tests have been reorganised to follow the definition's structure.
* Documentation has been improved
* Added structures for resource definitions, natural resources
definitions, resource providers, empire resources and empire mining
settings (both empire-wide and planet-specific).
* Added a few common utility functions to the SQL test suite. These
functions allow test initialisation to be a little shorter.
* Added "MINE" production type and an associated building definition.
The production will not be added to the XML dump or to the output of the
planets summary page, as this is extremely temporary.
