Restricts the child program's access based on the entries in the config file.
If no config provided as params, checks the current directory for .fendrc. If not found checks in ~/.fendrc. If not found, throws an error
{mode} {file}
mode is a octal 3 digit number (RWX).
Eg.
777 represents all access to the {file}
000 represents no access to the {file}
./fend {absolute path to the program} [-c {config file name}]