v0.35.1: performance, AGPL licensing and documentation overhaul

- Web Server reads static files inline; proxy middleware chain flattened
- About window with license summary and project links; AGPL-3.0-or-later
- Rewritten documentation: feature list, screenshots, performance guide
- Fix false spikes in per-Vhost request-rate charts

src/cache/model/views.rs

@@ -77,7 +77,7 @@ fn retention_deadline(
 }
 
 fn has_validator(headers: &HeaderMap) -> bool {
-    headers.contains_key("etag") || headers.contains_key("last-modified")
+    headers.contains_key(::http::header::ETAG) || headers.contains_key(::http::header::LAST_MODIFIED)
 }
 
 fn stale_forbidden(must_revalidate: bool, proxy_revalidate: bool) -> bool {