Replace [v]asprintf with [v]snprintf for better portability

Functions [v]asprintf are not available for strawberry perl
Substitute with better standardized [v]snprintf functions
[Sass.xs] Clean up the error handling with a bit of DRY.
[Changes, Sass.pm] Version 0.8.0
[Build.PL] Windows can't do pipe open well.

Doesn't matter, we're not actually releasing from windows, just testing.