rename xfer<T> class to Xfer<T>
- The capitalization is consistent with most other template classes, but more importantly frees up xfer() for use as method name without needing special treatment to avoid ambiguities. It seems reasonable to have different names for transfer(...) and xfer() methods, since the transfer is occuring in different directions. The xfer() method can thus replace the recently introduced zero-parameter transfer() methods. Other name candidates (eg, yield, release, etc.) were deemed too abstract.