`:encoding :utf-8` in `defsystem` forms

Hi,

This patch adds `:encoding :utf-8` to all `defsystem` forms.  This enables ASDF/Quicklisp to load the system even if the user's Lisp implementation's default external format is not set to UTF-8.

Without this patch, I, for one, am unable to load the system due to `read` decoding errors.