Add -b flag for debugging

For now this just prints messages to stderr, so the user should manually
redirect stderr to avoid breaking the ui. This can be later expanded
upon to provide debugging messages in the command window.

Signed-off-by: Loui Chang <louipc.ist@gmail.com>
doc/toxic: Add missing flags and sort alphabetically.

Signed-off-by: Loui Chang <louipc.ist@gmail.com>
Clarify function of -b switch.

Signed-off-by: Loui Chang <louipc.ist@gmail.com>
Merge pull request #223 from louipc/master

Add debug flag and update man page.
allow resuming of broken file transfers (needs testing)