Use go embed for web files and remove httptreemux (#382)

- replace togo with go embed
- replace httptreemux with gin

closes #308

web/web.go

@@ -0,0 +1,44 @@
+package web
+
+import (
+	"embed"
+	"io/fs"
+	"io/ioutil"
+	"net/http"
+)
+
+//go:embed dist/*
+var webFiles embed.FS
+
+func HttpFS() http.FileSystem {
+	httpFS, err := fs.Sub(webFiles, "dist")
+	if err != nil {
+		panic(err)
+	}
+
+	return http.FS(httpFS)
+}
+
+func Lookup(path string) (buf []byte, err error) {
+	file, err := HttpFS().Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	buf, err = ioutil.ReadAll(file)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf, nil
+}
+
+func MustLookup(path string) (buf []byte) {
+	buf, err := Lookup(path)
+	if err != nil {
+		panic(err)
+	}
+
+	return buf
+}