Incorrect use of unreachable!()

[dtolnay]

extern crate byteorder;

fn main() {
    byteorder::LittleEndian::default();
}

thread 'main' panicked at 'internal error: entered unreachable code'

Unreachable doesn't mean "please don't call this," it means "you can't get here." I think it is okay for this method to panic but it should be something other than unreachable. A handwritten message explaining why this method exists would be nice.

cc @fitzgen

[frewsxcv]

Why does this Default implementation need to exist?

[BurntSushi]

@frewsxcv So that it works with derive seamlessly. See #52.