I've set `lexical-binding` to `nil` in all Emacs Lisp files to suppress
the warnings introduced in Emacs 31 requiring all elisp files to have a
`lexical-binding` comment.
This retains the default behavior of dynamic binding when no
`lexical-binding` comment is present. With it set to `t` across the
board, various things break, and fixing those is a task for another day.
As flycheck uses the right fringe to indicate warnings/errors, the
default rightward pointing arrow never made much sense. This replaces it
with a custom leftward facing double-arrow so it actually points back at
the code in question.
