Add template parameters to JsCode objects

Is your feature request related to a problem? Please describe.
I'd like to be able to refer to other folium /leaflet objects inside a JsCode object. So far I have been using string interpolation inside the body of the JsCode object.

Describe the solution you'd like
I'd like to add parameters to the JsCode __init__ method, together with a basic string templating solution. For the string templating I'd prefer to use the good-old %(name)s format.

Describe alternatives you've considered
I considered using the newer formatting templates such as used in python format, or Jinja templates. However, due to brace heavy nature of javascript, I think a completely new variable marker will lead to more readable code.

Implementation
folium is maintained by volunteers. Can you help make a PR if we want to implement this feature?

首先阅读 JsCode init 入口点以及 JsCode 主体中当前对字符串插值的使用方式。将所请求的 %(name)s 参数行为与现有的 JavaScript 生成方式进行比较。当 JsCode 接受参数并使用提议的基本模板格式对其进行渲染，同时为新行为提供覆盖测试时，即可视为完成。