Release v1.8.0

• Migrate to Manifest V3 (#179).
• Integrate macro_railroad_ext (#183). Kudos to @lukaslueg.

• Support options page. Fixes (#133).
• Replace 'crate:check' action with chrome.storage API query.
• Support the new search-index loading, see rust-lang/rust#98124.
• Add more books into :book command. Thanks .
• Add :book/zh command to list Chinese books. (#175).
• Adjust margin of add to extension button (#178).
• Remove uninstall url. Close (#188).
• Bugfix:
  • Fix default offlineDocPath undefine bug.
  • Don't load search index in non-rust doc pages
  • Invalid cached crate searcher after crate search index updated or removed.

Thanks for the contributions from @C-Dao, @zjp-CN, and @ZhangHanDong.