Set fee

[raphjaph]

No description provided.

[casey]

Let's also add a fee rate wrapper type:

struct FeeRate(u64);

impl FromStr for FeeRate {
   // parse an f64
   // check for bad values
   // Self((v * 1000.0).round() as u64)
}

impl FeeRate {
  fn fee(vbytes: u64) -> Amount {
   Amount::from_sat(((self.0 as f64) / 1000.0 * vbytes as f64).ceil() as u64)
  }
}