fix spacing issue in generated torrc files

refs #112
space out authority booting

refs #112
dont generate new configs with MaxOnionsPending

refs #127
better handling of tor logging

instead of intercepting Tor's logv(), use the add_callback_log()
to register a log callback that we can then use to direct log
messages through Shadow's logging facilities.

this happens automatically, so we no longer have to tell Tor to
log to stdout. tor's log messages are currently filtered based
on shadow's configured log level, but scallion can take a log
level input if we need that to change.

refs #128
fix format string error

closes #128