Added helper macros.

[BradWBeer]

I added with-surface, with-context-from-surface and with-surface-and-context macros which I use to make life easier with cl-pango. cl-pango was a part of clinch, but I'm moving it away so it's useful to other libraries. I've used these macros in clinch and they help prevent errors when transient creating surfaces.

Currently I export these symbols through cl-pango in an (in-package ..) and (export ...). This shouldn't be an issue considering it's an experimental library.

[rpav]

I feel like this should optionally not destroy the surface (maybe use &key not &optional for further extension). Also, there's no (defvar *surface*) afaict, which there probably should be, even if it's not really used elsewhere else (yet!).

[BradWBeer]

I agree. I must have defvared surface somewhere in cl-pango. I also wanted to discuss with-context. It seems like the context should be destroyed at the end. Whatever the case, with-context and with-surface should work the same to limit surprises.