Updated push logic to use jsontool (https://github.com/trentm/json).

This solves a problem with devices with names that have spaces and makes
the access of JSON object values easier, especially if PushBullet decides
to make "unpretty" the JSON returned from the API endpoints.
Added requirement for jsontool
Updated list function to leverage jsontool
Changed to allow exported $CONFIG variables to be set externally
to the script, allowing scripts running as different users to
send Pushbullet notifications using a line similar to the following
(in Bash):

$ CONFIG=/some/other/path/pushbullet bash -c "pushbullet push \"Device\" note \"Title\" \"Body\""
Updated authors & added example of inlining config file before invoking.
Merge pull request #5 from zerodivide1/master

Fixed Devices with spaces in name & leverage jsontool