Better handling of relative subimports
Better handling of relative subimports

The old way of handling sub imports didn't actually allow them to be
relative, which is half the power of the import package.

The new code correctly identifies all my subimported texfiles in
a pretty complicated latex project.

kmarius/vimtex,lervag/vimtex,lervag/vimtex,Aster89/vimtex,Aster89/vimtex,kmarius/vimtex