chroot implementation

This is an implementation for chroot command-line utility (issue #249)
I made it compatible with both BSD and GNU command-line parameters.

Ah, sorry, I didn't notice this before.  You don't need the braces here.  You can just put a comma after ```defaultShell```.  You really don't need the braces anywhere where you have a match with only one expression (so this also applies to the next line, [line 82](https://github.com/uutils/coreutils/pull/252/files#diff-59a9b358013d28f22cd5c32291b49f8dR82), [line 108](https://github.com/uutils/coreutils/pull/252/files#diff-59a9b358013d28f22cd5c32291b49f8dR108), and maybe a couple of other lines (if I missed them).