Refactor and update RocketChat bridge

* Add support for editing/deleting messages
* Add support for uploading files
* Add support for avatars
* Use the Rocket.Chat.Go.SDK
* Use the rest and streaming api

vendor/github.com/nelsonken/gomf/form_builder.go

@@ -0,0 +1,89 @@
+package gomf
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"mime/multipart"
+	"net/http"
+	"net/textproto"
+)
+
+type FormBuilder struct {
+	w *multipart.Writer
+	b *bytes.Buffer
+}
+
+func New() *FormBuilder {
+	buf := new(bytes.Buffer)
+	writer := multipart.NewWriter(buf)
+	return &FormBuilder{
+		w: writer,
+		b: buf,
+	}
+}
+
+func (ufw *FormBuilder) WriteField(name, value string) error {
+	w, err := ufw.w.CreateFormField(name)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write([]byte(value))
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// WriteFile if contentType is empty-string, will auto convert to application/octet-stream
+func (ufw *FormBuilder) WriteFile(fieldName, fileName, contentType string, content []byte) error {
+	if contentType == "" {
+		contentType = "application/octet-stream"
+	}
+
+	wx, err := ufw.w.CreatePart(textproto.MIMEHeader{
+		"Content-Type": []string{
+			contentType,
+		},
+		"Content-Disposition": []string{
+			fmt.Sprintf(`form-data; name="%s"; filename="%s"`, fieldName, fileName),
+		},
+	})
+	if err != nil {
+		return err
+	}
+
+	_, err = wx.Write(content)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (fb *FormBuilder) Close() error {
+	return fb.w.Close()
+}
+
+func (fb *FormBuilder) GetBuffer() *bytes.Buffer {
+	return fb.b
+}
+
+func (fb *FormBuilder) GetHTTPRequest(ctx context.Context, reqURL string) (*http.Request, error) {
+	err := fb.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	req, err := http.NewRequest("POST", reqURL, fb.b)
+	if err != nil {
+		return nil, err
+	}
+
+	req.Header.Set("Content-Type", fb.w.FormDataContentType())
+	req = req.WithContext(ctx)
+
+	return req, nil
+}