Cleanup

Small tasks to be done before bumping the version number:

• change pldoc alias from __API__ to _API_ (consistent with default aliases)

• move version.pl to root directory (more prominent position)

• export version number under other name (this_version/1 is rather uncommon), or export api_version//0 instead

• remove mockups

• remove unused predicates?

• define and use location background?

• verify schemata

• provide curls?