Is there any reason to we have got the `pdf_fsys_create' procedure?
It is supposed do:
-- Function: pdf_fsys_t pdf_fsys_create (struct pdf_fsys_impl_s IMPLEMENTATION)
Create and return a new filesystem variable that will use a given
implementation.
which copy the `pdf_fsys_impl_s' structure.
I think we could assume pdf_fsys_t is a pointer to pdf_fsys_impl_s
(rename pdf_fsys_impl_s to pdf_fsys_s), in order to the library can
provide PDF_FSYS_DISK, PDF_FSYS_HTTP, etc, to use as pdf_fsys_t
directly.
If you agree, I will change this.
