MINOR: sample: add rtrim converter

This converter strips specified characters from the end of a string.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index c8e9cbc..b52ea17 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -14442,6 +14442,10 @@
             "http-response capture", "capture.req.hdr" and
             "capture.res.hdr" (sample fetches).
 
+rtrim(<chars>)
+  Skips any characters from <chars> from the end of the string representation
+  of the input sample.
+
 sdbm([<avalanche>])
   Hashes a binary input sample into an unsigned 32-bit quantity using the SDBM
   hash function. Optionally, it is possible to apply a full avalanche hash
diff --git a/src/sample.c b/src/sample.c
index fbbdab1..c26882d 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -3015,6 +3015,26 @@
 	return 1;
 }
 
+/**/
+static int sample_conv_rtrim(const struct arg *arg_p, struct sample *smp, void *private)
+{
+	char *delimiters, *p;
+	size_t dlen, l;
+
+	delimiters =  arg_p[0].data.str.area;
+	dlen = arg_p[0].data.str.data;
+
+	l = smp->data.u.str.data;
+	p = smp->data.u.str.area + l - 1;
+	while (l && memchr(delimiters, *p, dlen) != NULL) {
+		p--;
+		l--;
+	}
+
+	smp->data.u.str.data = l;
+	return 1;
+}
+
 /************************************************************************/
 /*       All supported sample fetch functions must be declared here     */
 /************************************************************************/
@@ -3486,6 +3506,7 @@
 	{ "htonl",    sample_conv_htonl,              0, NULL, SMP_T_SINT, SMP_T_BIN  },
 	{ "cut_crlf", sample_conv_cut_crlf,           0, NULL, SMP_T_STR,  SMP_T_STR  },
 	{ "ltrim",    sample_conv_ltrim,    ARG1(1,STR), NULL, SMP_T_STR,  SMP_T_STR  },
+	{ "rtrim",    sample_conv_rtrim,    ARG1(1,STR), NULL, SMP_T_STR,  SMP_T_STR  },
 	{ NULL, NULL, 0, 0, 0 },
 }};