Merge pull request #27 from lukaslueg/master

Graphviz may not be available during tests
note about graphviz cleanup
update tests, coverage stats
add test

coverage for when the TorConfig passed to a TCP4HiddenServiceEndpoint is already
bootstrapped when listen() is called.
Merge pull request #28 from lukaslueg/master

Fix for Issue #26 and a whole bunch of pep8 and style, plus a test for IP to int converter, all from lukaslueg
fix whitespace errors
notes about lukaslueg's recent fixes
issue #30; make ipaddr module actually-optional
note about issue #30 fix
temporary fix for pre-2.7 Pythons (which lack subprocess.check_output)