Changes to auto stop spinner after fix interval

Added 2 parameters:
1) Autostop?: boolean(default false) - to specify if spinner should be automatically stopped or not
2) Stoptimer?: number(default 7000) - to specify the time to stop the timer automatically after specified milliseconds (7000-> 7 sec)

On starting the spinner, if the autostop is set to true then the spinner would get stop automatically after 7 sec(default) or by given interval in Stoptimer parameter of the spinner instance.

This changes resoved my issue to stop spinner automatically if server fails to response that I have specified in Issue #268 https://github.com/fgnass/spin.js/issues/268