enable jekyll-seo-tag plugin, set site language

revert-main.scss

misc pages: add category, change layout

- add category to `site.md`
- change layout on `devvyn.md` from `post` to `page`

override default layout to add txtpen support

Revert "override default layout to add txtpen support"

This reverts commit db87d20

fixup! rename files in pages

move philips hue lets play to _play/_drafts

convert scss to sass

rename files in pages

add a site dateline to the footer