The list was out of date and the paragraph already refers to the
CURLOPT_HTTPAUTH explanation. All the auth bits are explained properly
there.

It also removes the ambiguity for what the "added" phrase refers to.

This change based on pull request #85 on github

URL: https://github.com/bagder/curl/pull/85
Reported-by: gnawhleinad

error: 'MULTI_PERFORM_HANG_TIMEOUT' undeclared

Simplified the SMTP multi example as this example should demonstrate
the differences the easy and multi interfaces rather than introduce new
concepts such as user authentication and TLS which are shown in the TLS
and SSL examples.

Updated to read data from a callback rather than from stdio as this is
more realistic to most use cases.

Replaced the use of CURLOPT_USERPWD for the preferred CURLOPT_USERNAME
and CURLOPT_PASSWORD options and used the same username and password for
all email examples which is the same as that used in the test suite.