Add Option, Trace, and Connect HTTP methods

* Add HTTP verbs per RFC 7231 and RFC 5789

README.md

@@ -45,7 +45,7 @@ Use `Path` to set or extend the URL for created Requests. Extension means the pa
 req, err := sling.New().Base("https://example.com/").Path("foo/").Path("bar").Request()
 ```
 
-Use `Get`, `Post`, `Put`, `Patch`, `Delete`, or `Head` which are exactly the same as `Path` except they set the HTTP method too.
+Use `Get`, `Post`, `Put`, `Patch`, `Delete`, `Head`, `Options`, `Trace`, or `Connect` which are exactly the same as `Path` except they set the HTTP method too.
 
 ```go
 req, err := sling.New().Post("http://upload.com/gophers")

sling.go

@@ -137,6 +137,24 @@ func (s *Sling) Delete(pathURL string) *Sling {
 	return s.Path(pathURL)
 }
 
+// Options sets the Sling method to OPTIONS and sets the given pathURL.
+func (s *Sling) Options(pathURL string) *Sling {
+	s.method = "OPTIONS"
+	return s.Path(pathURL)
+}
+
+// Trace sets the Sling method to TRACE and sets the given pathURL.
+func (s *Sling) Trace(pathURL string) *Sling {
+	s.method = "TRACE"
+	return s.Path(pathURL)
+}
+
+// Connect sets the Sling method to CONNECT and sets the given pathURL.
+func (s *Sling) Connect(pathURL string) *Sling {
+	s.method = "CONNECT"
+	return s.Path(pathURL)
+}
+
 // Header
 
 // Add adds the key, value pair in Headers, appending values for existing keys

sling_test.go

@@ -196,6 +196,9 @@ func TestMethodSetters(t *testing.T) {
 		{New().Put("http://a.io"), "PUT"},
 		{New().Patch("http://a.io"), "PATCH"},
 		{New().Delete("http://a.io"), "DELETE"},
+		{New().Options("http://a.io"), "OPTIONS"},
+		{New().Trace("http://a.io"), "TRACE"},
+		{New().Connect("http://a.io"), "CONNECT"},
 	}
 	for _, c := range cases {
 		if c.sling.method != c.expectedMethod {