DOC, STY: Added documentation, also some formatting.

doc/table_structure.md

patches/patch20200710-3.0.0-rc2/fix_unversioned.sql

patches/patch20200710-3.0.0-rc2/versioning.sql

procedures/deleteEntityProperties.sql

procedures/deleteIsaCache.sql

procedures/entityVersioning.sql

procedures/insertEntity.sql

procedures/insertEntityProperty.sql

procedures/retrieveEntity.sql

procedures/retrieveEntityOverrides.sql

procedures/retrieveEntityParents.sql

procedures/retrieveEntityProperties.sql

procedures/updateEntity.sql

tests/test_0_setup.sql

tests/test_entity_versioning.sql

tests/test_insert_update_delete.sql

tests/test_reference_values.sql