In a file grades.py, create a function
convert_to_letter_grade.  The function takes a numeric
grade from 0 to 100, and 
prints the associated letter grade using the following scale:
Note that square brackets mean inclusive, and parenthesis means exclusive.
Create a Python function called
batting_average(appearances) in a file with the same
name. The function parameter, appearances, is a list of ints 
that encodes the results of a baseball player's appearances at
batting. Each plate appearance can be interpreted as follows:
| 4 | Home Run | 
| 3 | Triple | 
| 2 | Double | 
| 1 | Single | 
| 0 | Walk | 
| -1 | Out | 
The function should return the batting average for the plate appearances in the list. The batting average can be computed using the following equations:
  at_bats = plate_appearances - walks
  hits = singles + doubles + triples + home_runs
  batting_average = hits / at_bats
>> print(batting_average([1, 1, -1])) 0.6666666666 >> pedroia_at_bats = [-1, 1, -1, -1, 1, -1, -1, 2, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, 0, -1, 0, -1, -1, -1, 2, 1, -1, -1, -1, -1, 1, 0, -1, -1, -1, 1, -1, -1, 1, -1, 1, -1, 0, -1, 1, 1, -1, -1, 2, 0, -1, -1, -1, -1, -1, -1, -1, 1, -1, 2, -1, -1, -1, -1, -1, -1, -1, 1] >> print(batting_average(pedroia_at_bats)) 0.25396825396825395