We may only have had just a small taste of what Saturday Night Live is like to have on our screens on a weekly basis, thanks to the admittedly very good UK version launching this year, but over the pond, it is a six-decade institution that has launched some truly stellar careers. It is also a pretty cutthroat place to try to make your way as a young up-and-coming comedian, as many have discovered since the programme began back in 1975 with a cas…