define-constant so that a type could optionally be added.
Copied and renamed two functions from PORT ext.lisp ("extensions"), which allow for automatically generation
definline clauses on defuns, and for defining global variables with type similarly less verbosely.
defcustom is for defining global variables with type.
Includes tests. I didn't modify any code in alexandria to use these, but I defined them in the first file (definitions.lisp) in the asd, so they could be used throughout if wanted.
Looking to also do shell.lisp and sys.lisp (select functions that fit alexandria's goal). I hope this will be accepted.