Simplify Less application boilerplate

Add a Config subclass with simplified configuration that will be used by
default by any Kelp::Less application. This configuration will not load
any modules or middleware, leaving it up to the user to manually load
any modules needed.

Additionally, bin/Kelp --less <name> will now only generate the psgi
application, and not any other folders, views, templates etc.
Downgrade confess to croak and croak to die

Kelp::Response used confess and croak excessively. Both changed to die,
so that the user can control how much stack trace they want via the
'long_error' attribute or the KELP_LONG_ERROR env variable.
New Logger::Simple, remove Logger::StdErr

Logger::Simple can now be used in Kelp::Less (and Kelp) applications if
the goal is to only print everything to STDERR.