Update the manuals to reflect the new behavior of gfsec-split's
-c, --config option.
Use firstname.lastname@example.org as contact address in the manual; update the
URL for the Gitweb interface.
This chapter should contain real use cases for Gfsecret. For now,
it describes the use of Gfsecret for keeping a GnuPG primary key
offline, because that was my primary motivation for this project.
This is an almost complete rewrite.
Complement the man pages and the README with a TeXinfo manual.