Fix: Get rid of "TeX-PDF-mode is not known to be defined" warning that
comes up when byte-compiling init.el.
Turn on eldoc-mode in lisp-interaction-mode.
Set up key bindings for `eval-buffer` and `eval-region`.

These key bindings are (currently) local to emacs-lisp-mode (and child
modes, e.g. lisp-interaction-mode).