use filepath.Join wrapper for different embed and os path styles

If using internal, "/" is used as a separator always, and with external,
filepath.Join is used.

embed.py

@@ -35,6 +35,11 @@ type rewriteFS struct {
 func (l rewriteFS) Open(name string) (fs.File, error)          { return l.fs.Open(l.prefix + name) }
 func (l rewriteFS) ReadDir(name string) ([]fs.DirEntry, error) { return l.fs.ReadDir(l.prefix + name) }
 func (l rewriteFS) ReadFile(name string) ([]byte, error)       { return l.fs.ReadFile(l.prefix + name) }
+func FSJoin(elem ...string) string {
+    out := ""
+    for _, v := range elem { out += v + "/" }
+    return out[:len(out)-1]
+}
 
 func loadFilesystems() {
 	langFS = rewriteFS{laFS, "lang/"}
@@ -53,6 +58,8 @@ import (
 var localFS fs.FS
 var langFS fs.FS
 
+func FSJoin(elem ...string) string { return filepath.Join(elem...) }
+
 func loadFilesystems() {
     log.Println("Using external storage")
     executable, _ := os.Executable()