Release v1.12.0

• Update search index
• docs: add doc on how to enable offline mode (#253)
• Fix macro diagram not showing in some crates (#256)
• Fix redirection issue when searching in std documentation (#258)
• Fix getVars(), close #259
• Fix html escape lint descriptions
• Fix call start() twice. Close #260.

Thanks for the contributions from @Devin-Yeung and @SteveLauC.