The `address::Error` is module level general, we can make the code
easier to maintain and easier to stabalize by splitting the parse error
out of the general error.
Create a `ParseError` that is returned by `FromStr for Address`. Remove
the now unused variants from the general `address::Error`.
In an effort to reduce the number of lines of code import the error
variants locally within the `Display` impl on `Error`.
Refactor only, no logic changes.
Split the error code out of `address/mod.rs` and into
`address/error.rs`. Code move only, no changes other than to
imports/exports etc. to make it build.
Tobin C. Harding