MINOR: converter: adding support for url_enc

add base support for url encode following RFC3986, supporting `query`
type only.

- add test checking url_enc/url_dec/url_enc
- update documentation
- leave the door open for future changes

this should resolve github issue #941

Signed-off-by: William Dauchy <wdauchy@gmail.com>
(cherry picked from commit 888b0ae8cf92cb23112bd8920b256b0bdf67caf0)
[wt: updated regtest to mention 2.3]
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 362a2fb..6c0baf6 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -16023,6 +16023,12 @@
   space (' '). Otherwise this will only happen after a question mark indicating
   a query string ('?').
 
+url_enc([<enc_type>])
+  Takes a string provided as input and returns the encoded version as output.
+  The input and the output are of type string. By default the type of encoding
+  is meant for `query` type. There is no other type supported for now but the
+  optional argument is here for future changes.
+
 ungrpc(<field_number>,[<field_type>])
   This extracts the protocol buffers message field in raw mode of an input binary
   sample representation of a gRPC message with <field_number> as field number