Change TODO to markdown file
Fix issue where relative path needs to be converted to absolute path

This problem is caused because the copy_files subroutine tries to copy files
*while* scanning for files. PWD of the program changes while it is scanning
through directories, thus, copy() can't find the files and directories if
relative paths are used. As a solution, copy_file() is renamed to
add_files_to_copy which adds the partial path under $from to copy (so that the
destination path can be easily created by concatenating the $to) and later
using the copy_files() to copy the files to the destination.
Allow backing up the source by adding command line options

Tar archives are created with the specified prefix.
Improve help messages and comments for readability