MINOR: uri_normalizer: Add a `merge-slashes` normalizer to http-request normalize-uri

This normalizer merges adjacent slashes into a single slash, thus removing
empty path segments.

See GitHub Issue #714.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 4241f92..4dec9c8 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -6011,6 +6011,19 @@
 
   See RFC 8297 for more information.
 
+http-request normalize-uri <normalizer> [ { if | unless } <condition> ]
+http-request normalize-uri merge-slashes [ { if | unless } <condition> ]
+
+  Performs normalization of the request's URI. The following normalizers are
+  available:
+
+  - merge-slashes: Merges adjacent slashes within the "path" component into a
+      single slash.
+
+      Example:
+      - //        -> /
+      - /foo//bar -> /foo/bar
+
 http-request redirect <rule> [ { if | unless } <condition> ]
 
   This performs an HTTP redirection based on a redirect rule. This is exactly