[PYTHON] Add jinja2 filter in responder 2.0.0 or later

TL;DR

Responder became Ver 2.0.0 and jinja_env disappeared from api and I was in trouble because I could not use custom filter, so I will solve it so that it works for the time being

custom filter and html

custom_filters.py

def css_filter(path):
    return f"./static/css/{path}"

_layout.html

...
<link rel="stylesheet" href="{{ 'style.css' | css }}">
...

Until 1.3.2

Until 1.3.2, filters could be added using the following writing method.

app.py

import responder
import custom_filters

api = responder.API()


api.jinja_env.filters.update(
    css=custom_filters.css_filter
)

2.0.0 or later

Since there is no jinja_env after 2.0.0, I edited it as follows for the time being

app.py

import responder
import custom_filters

api = responder.API()


api.templates._env.filters.update(
    css=custom_filters.css_filter
)

Since it has _, it may not be recommended to refer to it as a responder ...