Solved problem 0004: Word count in text file

[gouriphadnis0301]

This pull request adds a solution for Problem 0004 from the "Show-Me-the-Code" Python exercises.

Key features of the solution:

1. Reads a plain text file and counts the occurrence of each word.
2. Cleans punctuation and converts all words to lowercase for accurate counting.
3. Prints the top 20 most frequent words in the console.
4. Saves the full word counts to a text file named 'word_count.txt'.
5. Demonstrates Python basics such as loops, string manipulation, file I/O, and usage of collections.Counter.

This solution is self-contained, easy to read, and can be run directly.