improve tmuxp load completions

1. Limit wildcard json/yaml file matches to current directory
2. Preserve all directory completion (for tabbing into directories)
3. Use unlimited depth search for directories with .tmuxp.(yaml/json)
   inside them. tmuxp load command can load the file or the directory.

src/_tmuxp

@@ -101,7 +101,8 @@ __tmuxp_load() {
       local s
       _alternative \
         'sessions-user:user session:compadd -F line - ~/.tmuxp/*.(json|yml|yaml)(:r:t)' \
-        'sessions-other:session in current directory:_path_files -g "**/*.(json|yaml|yml)(-.)"'
+        'sessions-other:session in current directory:_path_files -/ -g "**/.tmuxp.(yml|yaml|json)"' \
+        'sessions-other:session in current directory:_path_files -g "*.(yml|yaml|json)"'
       ;;
   esac
 }