Integrate shorthand functionality into elisp-mode.el

Integrate shorthand functionality into elisp-mode.el

Also rename the main variable to elisp-shorthands, from the
silly pleonastic shorthand-shorthands.

For some reason, I had to stick the new source-file loading functions
in lisp/international/mule.el, otherwise lisp/loadup.el wouldn't see
them.  This should probably be fixed.

* lisp/shorthand.el: Remove.

* lisp/progmodes/elisp-mode.el (elisp--shorthand-load-wrapper):
Move here.

* src/lread.c (oblookup_considering_shorthand, syms_of_lread):
Rename variable elisp-shorthand, from shorthand-shorthands.

* test/lisp/shorthand-tests.el: Remove.

* test/lisp/progmodes/elisp-mode-tests.el (elisp-shorthand-read-buffer)
(elisp-shorthand-read-from-string)
(elisp-shorthand-load-a-file): New tests.

* test/lisp/progmodes/elisp-resources/simple-shorthand-test.el: New file

* lisp/loadup.el (load-source-file-function): Set to
  load-with-shorthands-and-code-conversion.

* lisp/international/mule.el (hack-elisp-shorthands): Move here.
(load-with-shorthands-and-code-conversion): And here.