Cleaned up in 434d1a210582a10d496d28598c280e07873a97b0

The idea was that you could override the `api_username` setting per call without having to re-instantiate the interface object. It will use the username in the `@api_username`, but can be overriden by an `:api_username` option passed in, e.g.,
```ruby
e = Lumberg::Cpanel::Email.new(
  :server            => lumberg_server,
  :api_username => "jerry"
)
e.add_account(
  :domain    => "jerry.com",
  :email       => "jerry",
  :quota       => 1000,
  :password => "T0ps3cr3t"
)
# Add another email account for a different user on the server
e.add_account(
  :api_username => "tom",
  :domain           => "tom.com",
  :email              => "tom",
  :quota              => 1000,
  :password        => "password"
```