Reword the header sections, show versions, and link to commits

[rwstauner]

Rework the tops of the pages to add more speedup ratios, clarify versions, and link to commits used.

Home page:

Run details:

Commits:

• Record more metadata of ruby when running benchmarks
• Rename prev yjit config var for consistency with other prev yjit var
• Make yjit_bench commit available to report template
• Make ruby and yjit-bench commits available to site collections
• Compute speedup for current yjit over previous yjit
• Add current yjit vs previous yjit speedup values to headline box
• Link to yjit-bench commit and yjit (ruby) commit
• Set page title
• Simplify footer html