imagesize 0.15.0

Quick probing of image dimensions without loading the entire file.
Documentation 
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use crate::{
    util::{read_u16, Endian},
    ImageResult, ImageSize,
};
use std::io::{BufRead, Seek, SeekFrom};

pub fn size<R: BufRead + Seek>(reader: &mut R) -> ImageResult<ImageSize> {
    reader.seek(SeekFrom::Start(6))?;

    Ok(ImageSize {
        width: read_u16(reader, &Endian::Little)? as usize,
        height: read_u16(reader, &Endian::Little)? as usize,
    })
}

pub fn matches(header: &[u8]) -> bool {
    header.starts_with(b"GIF8")
}