Provide variants of all interfaces with typed arguments

[jonhoo]

Most of the APIs we currently expose take &str arguments whose format is strictly dictated by RFC 3501. That's unfortunate, because it makes it easy for users to do things that are incorrect. Instead, we should write up typed versions of all those APIs (probably using the builder pattern) such that none of the APIs can be misused. We may want to just provide builders for the most common arguments, and then continue to expose string-only APIs for the more esoteric use-cases.

This should help with #74, and would be a good way to deal with #60.

See the original issue here: https://github.com/mattnenterprise/rust-imap/issues/99