v3.1.0

New

• Add alt attribute option to the post's preview image (#271)
• Add option lang to the site config

Improved

• Generate the breadcrumb by Liquid (drop the option site.defaults.breadcrumb in _config.yml)
• Remove /tabs/ from tabs path
• Exclude gemspec file from output
• Reduce Gemfile redundancy

Fixed

• Restore the prompt in the page nav button in the latest/oldest posts
• Fix post feature image bottom margin