Url Monitoring improvments

Some basic improvements

 * Fixed gem file
 * Check for valid status codes set to `200` as a default the others don't seem like sane defaults all the other 20* error codes shouldn't happen on a normal get and people shouldn't be monitoring urls that aren't successful by default. `HTTPServiceUnavailable` should NOT be a valid result HTTPFound might arguably be added to the default?
 * SSL checking is now on by default with the option to turn it of "secure by default". This is a breaking change but IMHO security should always be on by default
 * There is now a regex for checking the body's content. The default regex is set to accept any thing by default.

Hope this helps.