Now setting the minimum_confidence option in options.json allows the
user to control the minimum confidence a plugin must have to be executed
at all.  A value of null (the default) means all values greater than
zero are accepted.  All other values mean all confidences greater than
or equal to that value are accepted.

Previously, the default configuration file was only provided in a form
that was not included in distributions.  This could potentially
frustrate users by making it difficult to find a configuration file
example.  To remedy this, I moved it to be a package resource, imported
pkg_resources (setuptools is now a dependancy!), and made Kaylee load
both the default and the local configuration files, with the local of
course overriding the default.