Implementation of Assignment2

Hello Professor, Kindly review my PR. I made some changes suggested by my code buddy Vince in previous PR's for this assignment and he mistakenly closed PR twice. Following changes are made :

added order batter in batter_avg_rolling table
Rearrangement of columns of batter_avg_rolling output table.
Added number of rows for each table -Changes in comments -updated README.md.

Output and number of rows are attached here: For historical batting average Historical_average row_historic

For annual batting average Annual_average Annual_rows

For rolling over 100 days batting average Rolling_average row_for_only_batter

nishusingh11 / machine-learning-engineering-bda696

Implementation of Assignment2 #4