lua_api.txt: Various fixes and improvements (#7945)

lua_api.txt: Various fixes and improvements (#7945)

* Add missing tables of registered things

* Eliminate some duplication

Registration functions in 'Registered definitions' section merged into
'Registration functions' section.

* Misc. fixes

* Add privilege definition table

* Remove not-special soil group from special groups

* Merge two registration functions sections

* Move 'added to' information to tables section

Also fix some capitalization and missing periods

* Minor fixes

* Split Registration functions into two subsections

And update Registered definition tables to match order

* Fixes