Make this application Linux & MacOS Compatible

[jaladh-singhal]

This application uses Windows API by including inbuilt windows.h in C to use Beep() function. We can:

1. Devise a way to incorporate Windows API in non-Windows OS so that Beep() function can be accessed by C compiler in those OSes.
   Or...
2. Use an alternative/equivalent function for Beep() - a function which intakes frequency value & time value to produce a sound beep.

Please add suitable code/ code files and create a PR or comment suggestive ways!