Motivation:

The `User-Agent` request header was not being sent due to a bug.

The havester lacks support for the `From` request header.

Both HTTP request headers are recommented by the Harvester's guidelines:

https://www.openarchives.org/OAI/2.0/guidelines-harvester.htm

Modification:

Fix bug with `User-Agent` header.  Add support for `From` header.

The `From` header takes an email address as an argument.  Rather than
requiring a configuration file, the code looks for likely places where
the user may have already configured their email address.

Result:

The OAI-PMH harvester more closely followes the corresponding
guidelines.