[feature] Gin enable gzip encoding (#405)

* add gin gzip dependency

* add gzip middleware to router

* go mod tidy

vendor/github.com/gin-contrib/gzip/gzip.go

@@ -0,0 +1,39 @@
+package gzip
+
+import (
+	"compress/gzip"
+
+	"github.com/gin-gonic/gin"
+)
+
+const (
+	BestCompression    = gzip.BestCompression
+	BestSpeed          = gzip.BestSpeed
+	DefaultCompression = gzip.DefaultCompression
+	NoCompression      = gzip.NoCompression
+)
+
+func Gzip(level int, options ...Option) gin.HandlerFunc {
+	return newGzipHandler(level, options...).Handle
+}
+
+type gzipWriter struct {
+	gin.ResponseWriter
+	writer *gzip.Writer
+}
+
+func (g *gzipWriter) WriteString(s string) (int, error) {
+	g.Header().Del("Content-Length")
+	return g.writer.Write([]byte(s))
+}
+
+func (g *gzipWriter) Write(data []byte) (int, error) {
+	g.Header().Del("Content-Length")
+	return g.writer.Write(data)
+}
+
+// Fix: https://github.com/mholt/caddy/issues/38
+func (g *gzipWriter) WriteHeader(code int) {
+	g.Header().Del("Content-Length")
+	g.ResponseWriter.WriteHeader(code)
+}