feat(template): remove `.txt` wrapper

BREAKING CHANGE: Removal of `.txt` CSS class may break your existing post layout. Now `.txt` is replaced with `main.content`, a global content wrapper. To fix layout breaks for your existing site: simply remove all `<div class=txt>` containers from your posts
feat: better Redcarpet configurations, add some useful Redcarpet extensions
fix(style): fix mismatched color variables
feat(style): add syntax highlight support

Now you can use Jekyll built-in highlighter: http://jekyllrb.com/docs/templates/#code_snippet_highlighting
fix(style): fix code block overflow scroll issue
feat(style): add a simple table style
Bump version to 24.0.4
chore: commets cleanup
refactor(style): unified font unit