Add ctools_export_crud_load_multiple()

The following patch adds a ctools_export_crud_load_multiple() function and also adds support for a 'load multiple callback' hook. I debated having ctools_export_crud_load() re-use ctools_export_crud_load_multiple() like our core single-load functions typically re-use the multiple load functions but this would have complicated logic with having to support both 'load multiple callback' as well as 'load callback'.

Found some documentation fixes.

And another.

I swear I'm gunna find them all.

Patching with cat on y our arms is hard.

Bumping API version as well.

Fixed error with the example mymodule_myobj_load_multiple() func.

Tagging that this came from the metatags sprint.