Implement cl object methods for Emacs interop

[Fuco1]

Each Elsa object should have two printing methods:

• one to serialize the object, in a way that this can be read back to reconstruct the object => object-write. Slots can have overriding printers via :printer property

• one to print the object in a human readable way (for debugger etc). We will always use the #<class some-readable-representation> format. => cl-print-object. For a class hierarchy when reasonable we can use top-level class, since this does not need to be readable back into lisp.

• some classes might have specialised methods, for example elsa-type needs serialization in a elsa-make-type compatible form (rather than a string?), and elsa-form should be able to turn into a lisp form.

• use eieio-override-prin1 as printer for object types so there is no useless indent

• rename elsa-tostring to elsa-to-string

• elsa-type

  • elsa-type-describe -> maybe return a form instead, which could then be turned into a string. So this would return lisp forms string (symbol) or (list string) which could be (format "%s" x).
  • cl-print-object => #<elsa-type string> or #<elsa-type (list string)> => single implementation for type using the "description" to print the actual type.
  • object-write => (elsa-type-string) or (elsa-type-list :item-type (elsa-type-string))

• elsa-form

  • elsa-form-print -> we already have elsa-form-to-lisp which can then be turned into string
  • cl-print-object => #<elsa-form :foo> or #<elsa-form (list :list 1) => single implementation for all the forms with just a prefix #<elsa-form.