Macro absorb 

macro_rules! absorb {
    ($sponge:expr, $($absorbable:expr),+ ) => { ... };
}

Individually absorbs each element in a comma-separated list of absorbables into a sponge. Format is absorb!(s, a_0, a_1, ..., a_n), where s is a mutable reference to a sponge and each a_i implements Absorb.