Fix -Wreserved-user-defined-literal error in C++11.

    error: invalid suffix on literal; C++11 requires a space between literal and identifier
          [-Wreserved-user-defined-literal]
          "Item size of buffer (%"PY_FORMAT_SIZE_T"d byte%s) does not match size of '%s' (%"PY_FORMAT_SIZE_T"d byte%s)",
                                  ^

Went to town, sorry if I got carried away.

Mark or anyone - I've left a few comments in the ReST for places where I
could not make the particular feature work, or where I wasn't sure on
naming.

tests pass when compiled and run manually.

fixes typo in memory view validation code