pack_file object
This method will extract a file from an open pack file back onto disk.
bool extract_file(string internal_name, string file_on_disk)
Parameters:
internal_name
The internal storage name of a file inside the pack.
file_on_disk
The filename to use when extracting back onto disk.
Return value:
true on success, false on failure.
Remarks:
This method will work on a pack file opened for reading.
Example:

    // Open a pack file and extract some files.

    void main()
    {
    pack_file test;
    test.open("pack.dat");
    test.extract_file("t1","test1.txt");
    test.extract_file("t2","test2.txt");
    test.extract_file("t3","test3.txt");
    test.close();
    }