Many thanks to Chunglee Kim and Evan Kean who read and provided very useful comments on this revised review, and to Scott Ransom and Matthew Bailes for providing unpublished data given in Table 4. I am indebted to a number of colleagues who, as noted in many of the figure captions, kindly gave permission to use their figures in this article. Frequent use was made of NASA’s magnificent Astrophysics Data System , the arXiv e-print service  and of course the Google during the literature searches. My research is partially supported by West Virginia EPSCoR through a Research Challenge Grant. Finally, I would like to thank the Living Reviews editors for their support and patience during the completion of this long-overdue update.
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