title: how to visualize multiple json files with mapboxgl-jupyter?
body: <p>let's say I have two json files:</p>
  
  <pre><code>file_A = 'file_A.json'
  file_B = 'file_B.json'
  </code></pre>
  
  <p>I can use mapboxgl-jupyter for one file as following:</p>
  
  <pre><code>from mapboxgl.utils import *
  from mapboxgl.viz import *
  
  viz = ChoroplethViz(file_A, 
                      access_token=MAPBOX_TOKEN,
                      color_property='contenance',
                      color_stops=create_color_stops([0, 500, 1000, 5000, 10000], colors='YlOrRd'),
                      color_function_type='contenance',
                      line_stroke='-',
                      line_color= None,#'rgb(255,255,255)',
                      line_width=1,
                      opacity=0.9,
                      center=(3, 42.5),
                      zoom=7,
                      below_layer='waterway-label')
  viz.show()
  </code></pre>
  
  <p>But how to show both files on the same map?</p>
  
  <p>I have tried to merge all json files into one with <code>jsonmerge</code> but it often needs some extra care on how dicts are merged as it can make some mistakes.</p>