[cairo] Proposal: Splitting cairo.h for the backends

[Bill Spitzak]

Carl Worth wrote:

> Then the ps, pdf, and png backends also meet this definition with the
> exception of the currently contested FILE*.
> 
> Shall we leave these in cairo.h, or move them out as well for
> symmetry's sake?

I think they should be seperate.

The main header file should describe how to use a cairo_t and draw into 
it. A source file that includes only this header file can do all the 
drawing functions, but cannot create a cairo_t (except perhaps with some 
kind of clone-this operation). This is quite useful, because such source 
files can draw define functions that take a cairo_t as an argument, and 
draw into them.

Also I suspect any useful ps or pdf backend is going to have 
type-specific calls. I know that EPS has all kinds of comments about the 
page number and type and so on, calls to set this stuff would be useful, 
but certainly ps-specific.