Formatting changes

This fixes some formatting issues that annoyed me:

 * Use more intuitive qualified names for `Data.ByteString` modules

 * Clean up whitespace, particularly around `do` and `where`.  The most unsightly lines were:

  ```haskell
sendCommand (SMTPC conn _) meth =
    do bsPutCrLf conn command
       parseResponse conn
    where command = case meth of
                      (HELO param) -> "HELO " <> param
                      (EHLO param) -> "EHLO " <> param
                      ...
  ```

These commits change nothing but formatting.