A concise alternative to the file IO elisp idioms we're used to,
involving some combination of with-temp-file, with-temp-buffer,
insert-file-contents, coding-system-for-{read,write}, write-region, read
loops, print-to-current-buffer loops, etc.
These were engineered to make reading/writing text and lisp data from/to
files simpler, and will be used extensively in the v3 CLI.