Removing deprecated functionality can help to clean up the code a bit.
I remove the following deprecated functions and values:
* vector.zero
* vector.plane()
* vector.pos_to_string()
* vector.quickadd()
* vector.scalar()
* vector.get_data_from_pos()
* vector.set_data_to_pos()
* vector.set_data_to_pos_optional()
* vector.remove_data_from_pos()
* vector.get_data_pos_table()
Furthermore, I remove the unused, experimental vector_meta.lua file
and make luacheck linting more strict so that it can show accidental
uses of deprecated functions in the code of this mod if there are any.
This change can break compatility with old mods which use vector_extras.
