ISPC benchmarks

Results of the weekly benchmark run (benchmarks-weekly.yml, see benchmarks/README.md), one page per target:

• sse4-i32x4
• avx2-i32x8
• avx2-i32x16
• avx2-i16x16
• avx512gnr-x8
• avx512gnr-x16
• dispatch (16_dispatcher_overhead, auto-dispatch binary)

Pages of other targets from manual runs are at benchmarks/<target>/.