2.1.0

• Add small description text to help option (@kelson42)
• zimcheck: Better error reporting (@MiguelRocha, @kelson42)
• zimwriterfs: Update font mimetype (@kelson42)
• zimcheck: Fix various crash (@MiguelRocha)
• ci: Add building of deb package and publication on ppa (@legoktm)
• Add unit tests (@MiguelRocha, @asashnov)
• zimcheck: Handle data: urls correctly (@kelson42)
• zimcheck: Add testof empty links (@MiguelRocha)
• readme: Add link to packages links (repology) (@hashworks)
• zimwriterfs & zimrecreate: Add a option to write ZIM files using Zstandard
  compression (default lzma) (@kelson42)
• zimcheck: Performance improvement (@MiguelRocha, @veloman-yunkan)
• zimwriterfs: Create zim redirect entry when file is actually a symlink
  (@asashnov)
• zimcheck: Add a progress option (@kelson42)
• zimsplit: Use docopt to parse command line option (@MiguelRocha)
• zimwriterfs: Add a metadata M/Scraper with the name (zimwriterfs) and
  version of the scraper. (@asashnov)
• zimwriterfs: Do not allow to create a zim file inside the HTML source
  directory (@asashnov)
• zimcheck: Add internal integrity check using libzim validate
  (@veloman-yunkan)