added better subprocess interface

added subprocess interface that parses stdout to set attributes on
the object so that other Python programs know the state of the
current command. Also enables timeouts on commands (sends signal to
kill process at end of timeout)
added tcpdump primitive

added tcpdump primitive that interfaces with the tcpdump process
via the command module. This module implements a parser for some
of tcpdump's command line output and allows for the application of
simple post processing filters after the capture is complete (this
is advised to reduce PII)
updated for pep compliance
bug fix- typo in variable name from daemonize
added scheduler sync to backend

added a smart sync for the scheduler to the backend so that we
can get the latest frequency changes without overwriting our
last run time
added scheduler to centinel runtime

added a scheduler to the centinel runtime so that we can set
experiments to run with some frequency and we will preempt if we
are running the experiment too frequently. we are still dependent
on something like cron to run centinel itself, but this lets us
change the run frequency for individual experiments
fixed compatibility issue for SSL cert bundle string (unicode to ascii)
Merge pull request #101 from ben-jones/add_tcpdump

Add tcpdump
Merge pull request #102 from rpanah/cert_error_fix

fixed compatibility issue for SSL cert bundle string (unicode to ascii)
Merge pull request #100 from ben-jones/add_scheduler

Add scheduler