Added AMap(Gaode) provider with test and doc

[frees0l0]

Added AMap(Gaode as Chinese name) provider for geo search. An API key is needed to use this provider. See AMap GEO API Doc for details.

Usage:

import { AMapProvider } from 'leaflet-geosearch'

const provider = new AMapProvider({
      params: {
        key: process.env.AMAP_API_KEY, // Put your api key here
      },
    });

const results = await provider.search({ query: '上海市浦东新区外滩' });