Here's the script I wrote that automatically subscribes you to all forum threads. It's built to be run as a cron job.
You'll need to generate an API token for it which can be done at the bottom of the [profile settings page][profile]. It uses canvas's REST API to do the actual subscribing, the documentation for the api [is here][capi].
I also hate Canvas's WYSIWYG editor, so I wrote some scripts to render markdown, and then inline the styles. Typically I'll write my posts in a text file, and then run:
$ fpost name_of_file.md | pbcopy # pbcopy is an OSX thing, xclip -in works for xwindows.
and then just post the raw HTML into the WYSIWYG's 'html entry' portion.