Add initial Microsoft Teams support

Documentation on https://github.com/42wim/matterbridge/wiki/MS-Teams-setup

vendor/github.com/yaegashi/msgraph.go/jsonx/README.md

@@ -0,0 +1,55 @@
+# jsonx
+
+It's modified version of [encoding/json](https://golang.org/pkg/encoding/json/)
+which enables extra map field (with `jsonx:"true"` tag) to catch all other fields not declared in the struct.
+
+`jsonx` is a code name for internal use
+and not related to [JSONx](https://tools.ietf.org/html/draft-rsalz-jsonx-00).
+
+Example ([Run on playgroud](https://play.golang.org/p/TZi0JeHYG69))
+```go
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/yaegashi/msgraph.go/jsonx"
+)
+
+type Extra struct {
+	X     string
+	Y     int
+	Extra map[string]interface{} `json:"-" jsonx:"true"`
+}
+
+func main() {
+	var x1, x2 Extra
+	b := []byte(`{"X":"123","Y":123,"A":"123","B":123}`)
+	fmt.Printf("\nUnmarshal input: %s\n", string(b))
+	json.Unmarshal(b, &x1)
+	fmt.Printf(" json.Unmarshal: %#v\n", x1)
+	jsonx.Unmarshal(b, &x2)
+	fmt.Printf("jsonx.Unmarshal: %#v\n", x2)
+
+	x := Extra{X: "456", Y: 456, Extra: map[string]interface{}{"A": "456", "B": 456}}
+	fmt.Printf("\nMarshal input: %#v\n", x)
+	b1, _ := json.Marshal(x)
+	fmt.Printf(" json.Marshal: %s\n", string(b1))
+	b2, _ := jsonx.Marshal(x)
+	fmt.Printf("jsonx.Marshal: %s\n", string(b2))
+}
+```
+
+Result
+
+```text
+Unmarshal input: {"X":"123","Y":123,"A":"123","B":123}
+ json.Unmarshal: main.Extra{X:"123", Y:123, Extra:map[string]interface {}(nil)}
+jsonx.Unmarshal: main.Extra{X:"123", Y:123, Extra:map[string]interface {}{"A":"123", "B":123}}
+
+Marshal input: main.Extra{X:"456", Y:456, Extra:map[string]interface {}{"A":"456", "B":456}}
+ json.Marshal: {"X":"456","Y":456}
+jsonx.Marshal: {"X":"456","Y":456,"A":"456","B":456}
+```
+