Made the code more readable

[LeahScholten]

Made needlessly explicit returns implicit, put variables in the format string, removed an unnecessary check when handling user input, decreased indentation depth, replaced a return true with a return of the result of the comparison.

[LeahScholten]

Added the following modifications:
Derived Eq where possible for more flexibility, replaced the name of structs with Self in their functions for readability, made functions which don't influence other code const to add flexibility and readability, removed a clone of a String caused by a call to .to_owned(), made the start_playing function shorter by splitting it into multiple smaller functions, removed a redundant closure, removed async from a function without await, replaced an Option match with a map_or_else