Add access on a per role basis

Hi,

this is a great module you've written here!
Its allows the interface to be nicely simplified for users.

However it would have been nice for a more fine grained approach, where each section of a content-type form could be made invisible to each role individually, a bit like the matrix on the user permissions page.

for example authenticators users don't need to see url-path, but a website admin might need it.