* lisp/ses.el: Miscellaneous cleanups; use lexical-binding; avoid add-to-list.

* lisp/ses.el: Miscellaneous cleanups; use lexical-binding; avoid add-to-list.
(ses-localvars): Remove ses--local-printer-list, unused.
(ses--metaprogramming): New macro.  Use it to defvar variables.
(ses-set-localvars): Simplify.
(ses--locprn, ses-cell): Use defstruct.  Change ses-cell's
property-list into an alist.
(ses-locprn-get-compiled, ses-locprn-compiled-aset)
(ses-locprn-get-def, ses-locprn-def-aset, ses-locprn-get-number):
Remove; use defstruct accessors/setters instead.
(ses-cell-formula-aset, ses-cell-printer-aset)
(ses-cell-references-aset): Remove, use setf instead.
(ses--alist-get): New function.
(ses-cell-property): Rename from ses-cell-property-get and rewrite.
Use an alist instead of a plist and don't do move-to-front since the
list is always short.
(ses-cell-property-get-fun, ses-cell-property-delq-fun)
(ses-cell-property-set-fun, ses-cell-property-set)
(ses-cell-property-pop-fun, ses-cell-property-get-handle)
(ses-cell-property-handle-car, ses-cell-property-handle-setcar): Remove.
(ses--letref): New macro.
(ses-cell-property-pop): Rewrite.
(ses--cell): Rename from ses-cell and make it into a function.
Make `formula' fallback on `value' if nil.
(ses--local-printer): Rename from ses-local-printer and make it into
a function.
(ses-set-cell): Turn it into a macro so finding the accessor from the
field name is done at compile time.
(ses-repair-cell-reference-all): Test presence of `sym' rather than
`ref' before adding `sym' to :ses-repair-reference.
(ses-calculate-cell): Use ses--letref rather than
ses-cell-property-get-handle.
(ses-write-cells): Use a single prin1-to-string.
(ses-setter-with-undo): New function.
(ses-aset-with-undo, ses-set-with-undo): Rewrite using it.
(ses-unset-with-undo): Remove.
(ses-load): Prefer apply' over `eval'.
(ses-read-printer, ses-set-column-width): Use standard "(default
foo)" format.