Customize smart-dash-c-modes at startup

as doing it *after* turning smart-dash-mode on can result in a buffer
that should have the C-like hacks active not having them.
todo: replace "~/.emacs.d" with user-emacs-directory
Define .emacs.d-relative paths with user-emacs-dir

Also moves elisp-mode over to using my prog-mode hook, and fixes a few
elisp style errors flycheck showed me now that it's active in elisp buffers.

One of these days it'll be more widely used and I can just set it as my
prog-mode hook.