Implement `shutil` copy functions

[schwa]

The module shutil in the Python standard library defines several copy functions:

​http://docs.python.org/2/library/shutil.html#directory-and-files-operations
​http://docs.python.org/3/library/shutil.html#directory-and-files-operations

Of these, ftputil so far supports only copyfileobj. Although this is a fine building block for many kinds of copy operations (and used by ftputil for downloads and uploads), a bit more convenience (copy, copymode, copystat) wouldn't hurt.

There's also copytree but this obviously is a different complexity level than the above mentioned functions. Still, this would be nice to have.