Flymake Idiom Review of flywrite.el

Re-review the flymake manual on [Backend functions](https://www.gnu.org/software/emacs/manual/html_node/flymake/Backend-functions.html).

Review flywrite.el for idiomatic use of flymake.  Any non-idiomatic practices?  Are there any features in flymake that would make the flywrite code better or easier to understand?
