Find and format date headers

RFC 2822 defines the "Date:" header. It declares the header a required
part of an email message. The syntax for date headers is clearly laid
out. Stil, even a perfectly planned world has storms. The truth is, many
programs get it wrong. Very wrong. Or, they don't include a "Date:"
header at all. This often forces you to look elsewhere for the date, and
hoping to find something.

For this reason, the tedious process of looking for a valid date has
been encapsulated in this software. Further, the process of creating RFC
compliant date strings is also found in this software.