text: Title: Improve automatic bin determination for histograms
  Body: Currently, the formula for histogram binning sometimes results in bins that are very "skinny" and sometimes bins that are very "wide". We need to improve histogram bin width and size determination to ensure more accurate histograms are plotted. 
  This is especially true for the "Filter" action.
  
  
  Example: 
  ```python
  df = pd.read_csv("https://github.com/lux-org/lux-datasets/blob/master/data/olympic.csv?raw=True")
  df.intent=["Height"]
  df
  ```
  ![image](https://user-images.githubusercontent.com/5554675/104189469-aa3cd980-5455-11eb-94c6-06849b836e5a.png)
  
  ![image](https://user-images.githubusercontent.com/5554675/104189512-bd4fa980-5455-11eb-9eca-9dad6fb71ae7.png)
  
  This needs to be customized for matplotlib and Altair.