Convert Section trait to use Reader

[philipc]

I tried to keep the From<&[u8]>, but couldn't get it to work, eg something like:

// error[E0207]: the type parameter `Endian` is not constrained by the impl trait, self type, or predicates
impl<'input, Endian, T> From<&'input [u8]> for T
    where T: Section<EndianBuf<'input, Endian>>,
          Endian: Endianity
{
    fn from(v: &'input [u8]) -> Self {
        Self::from(EndianBuf::new(v))
    }
}

[coveralls]

Coverage decreased (-0.3%) to 93.393% when pulling ab3d9e0 on philipc:section into fdd6feb on gimli-rs:master.

[coveralls]

Coverage decreased (-0.3%) to 93.393% when pulling de2f1bd on philipc:section into fdd6feb on gimli-rs:master.

[fitzgen]

LGTM!

[fitzgen]

Why does this one need a turbo fish but the others don't?

[philipc]

Endian needs to be specified at least once, because it can't be inferred. But specifying it once is enough to let the rest be inferred.