Fix error when make outline summary.

[Haitham-AbdelKarim]

In the outline function, we iterate through each header and its paragraph. In each iteration, we pass this paragraph to functions that remove images, links, etc. But those functions accept the path of the README.md file, so the error "Invalid file. Only Markdown files (.md) are supported." raised.

To solve this problem, I changed the input parameter to accept the markdown content as a string and removed the reading file code from the implementation. I also checked if those functions are used in another place to avoid conflict and found that they are used only in the outline function.

Each function reads the file from given path. However, if we want to remove images, links, etc. from one README.md file, we need after each function call to write the output to the file again to be able to use the other functions, and it doesn't make sense.