exporting to a multi-layer format
Now, items are either
- placed onto the same layer as other items (simple items like labels, lines, pictures)
- placed onto the same layer as only other items of equal types (semi-complex items like scalebars or pages)
- placed onto their own unique layers (complex items like legends, maps)
Plus lots of tests covering this, where previously there was few
Checks whether a function declaration has parameters that are
top level const.
const values in declarations do not affect the signature of a
function, so they should not be put there.