I took this route on these code samples to bring it in line with the FFI examples, which likewise do not use the playpen.
generics: Fix typo (possessive missing apostrophe).
std_misc/file: Use samples, not playpens, for I/O examples.
Since the file samples aren't runnable, making them editable is not
particularly useful. Moreover, until #73 is closed, it will also make
those pages much easier to read in the sepia and night reading modes.
(rust_highfive has picked a reviewer for you, use r? to override)