prepare for version 0.013
ensure type is indx/PDL_Indx for indices into piddles
ensure type is indx/PDL_Indx for extent of dimensions
ensure type is indx/PDL_Indx for number of elements

Except xs/Iterator.xs, which we'll tackle in a separate commit.
rewrite _setnulltobad() to operate in-place
rewrite _istddev_post() to operate in-place
use IV instead of int for integral data in Iterator.xs
restore compatibility with non-64-bit PDL versions
add dependency on Test::PDL 0.10 for test_indx()
bugfix: do not put uninitialized value in $iter->{bin}
add section on 64-bit support to manual
update Changes
update Makefile.PL after Dist::Zilla upgrade
v0.013

 - added 64-bit support. PDL::NDBin will take advantage of 64-bit support with
   recent versions of PDL (2.007 or later), but should work with earlier
   versions, as well. Note that 64-bit support has not been tested very well
   yet, so it qualifies as 64-bit "safe" until I find time for more testing.
   But PDL::NDBin should now at least install on PDL 2.007 or later. (Edward
   Baudrez)