Pretty-print format for observation histogram

[JWCook]

Currently the histogram is just a dict, like:

{                    
    1: 8,  # January 
    2: 1,  # February
    3: 19, # March   
    ...,   # etc.    
}                    

It would be nice if pprint() handled this by printing out a formatted table like:

Month     Count 
━━━━━━━━━━━━━━━━
January   8     
February  1     
March     19    
...