Don't strictly depend on quicklisp by hardcoding quicklisp API code at the top of the file

[jgarte]

Hi,

Thanks for making this project!

I think we should not make sbcli strictly depend on quicklisp by hardcoding quicklisp specific code at the top of the file.

There are other package managers for Common Lisp such as Nix, Guix, Roswell, etc. that require the project to be in a package manager agnostic format.