Release v1.9.0

• Migrate to chrome.storage.onChange event to avoid add docs index failure (#206).
• Support search space-separated keywords.
• Cache feature flags in session storage.
• New commands:
  • :rustc - Search rustc codegen options and lints.
  • :target - Search rust target for three tiers.

• Add a pagination tip in the last page item.
• Remove prefix for RFC (??) & Improve docs (#197).
• Condense attributes and crates index size.
• Make feature flag's name sticky left.
• Bugfix:
  • Fix error code regex.
  • Fix incorrect export of stats/history (#203) (#204).
  • fix docs.rs show features (#209).
  • Fix source code navigate bug. Fix (#212).
  • Fix GitHub release page TOC compatibility (#214).

Thanks for the contributions from @shwin0901, @light4, and @xxchan.