The storage used will now be aligned to `VTKM_CACHE_LINE_SIZE bytes,
resulting in slightly better cache usage and load/store performance.
This define is set in `StorageBasic.h We also now detect if Posix is
available in Configure.h and will define VTKM_POSIX with _POSIX_VERSION
if it's available.

The AlignedAllocator used by StorageBasic is also STL compatible
and can be used in STL containers so user's can use it in their
std::vector and pass aligned user memory to the storage.