XCF File Reader

I wrote this for extracting layer and pixel data from XCF files for my game's art pipeline.

This library has a few notable limitations presently: - it always returns RGBA pixels; I have updated the methods to make this clear - this can also be fixed! I'll probably get around to it eventually. - it can only handle RGB or RGBA images, not grayscale or indexed, with or without alpha.

Tests needed. Contributions welcome.

Example

```rust extern crate xcf; use xcf::Xcf;

fn main() { let mut rdr = File::open("untitled.xcf") .expect("Failed to open file."); let raw_image = Xcf::load(&mut rdr) .expect("Failed to parse XCF file.");

// or simpler yet:
let raw_image = Xcf::open("untitled.xcf")
    .expect("Failed to open and parse XCF file.");

} ```