--extra-opts implemented for plugins

This patch implements --extra-opts argument for nagios plugins
as specified by http://nagiosplugins.org/extra-opts

New class: Parsers.ExtraOptsParser

PluginHelper has new command-line argument: --extra-opts

Fixes #54
Utils.reconsile_thresholds - new method to convert from new threshold syntax to current one
pynag.Utils - Code cleanup

PEP8 fixes
pynag.Plugins.PluginHelper - Implement timeout

Nagios developer guidelines require plugins to have a timeout
so --timeout is now built into PluginHelper.

I set a default timeout of 58 seconds, so plugins will exit with
status unknown right before nagios kills it.

Does anyone have thoughts on if a default timeout should be set or not ?
Improve unittests for ExtraOpts feature
Merge pull request #113 from pynag/feature-extra-opts

Feature extra opts, looking good!