Made the names of the functions to invoke the plugin the same.
This is a BREAKING change if using the lua mappings.
On the other hand, it should stay pretty stable for the foreseeable
future, with only new ones added and possibly vim commands added.
Should prepare the differentiation between a 'new' link and linking an
existing zetttel -- one is 'new_link' and one just 'makes_link' to
something else.