Authen::PluggableCaptcha is a fully modularized and extensible
system for making Pluggable Catpcha (Completely Automated Public
Turing Test to Tell Computers and Humans Apart) tests.
Pluggable? All Captcha objects are instantiated and interfaced via
the main module, and then manipulated to require various submodules
as plug-ins.
Authen::PluggableCaptcha borrows from the functionality in
Apache::Session::Flex.
