Function write_file_append 

pub fn write_file_append(path: &str, contents: &str) -> bool

Appends data to a file and returns a bool on success

Usage:

fsutils::write_file_append("text.txt", "Hello, world! ");
fsutils::write_file_append("text.txt", "Hi Again!");

assert_eq!(fsutils::read_file("text.txt"), "Hello, world! Hi Again!");