Httparse

- **PERF**: enable both compile-time and run-time checks for SSE4.2 and AVX2 instructions, and greatly improve parsing speed when available. See 40

- **FIX**: allow `HTAB` bytes in header values

- **FIX**: look for invalid version even if less than 8 bytes long, instead of returning `Status::Partial`

- **PERF**: switch header parsing to use lookup tables
- **PERF**: remove unused field when debug assertions aren't enabled

* **PERF** Reduce EOF checks in internal `parse_version`

- **FIXED**: overflow when parsing chunked size hex digit that was too big
- **FIXED**: allow parsing of response that do not include a reason-phrase