Enable region and offsets for Read/Write/Copy

[StRigaud]

For simplification, all call for memory accesses which takes an offset and a region are defined with defaults value (hard-coded).

Enabling none defaults value for these entries could simplify memory accessibility, e.g. __getitem__ and __setitem__ for the python wrapper.

ToDo:

• adapt read/write/copy call for both buffer and image using Rect buffer for OpenCL
• insure compatibility with CUDA
• clarify copy method behavior (see issue #96)
• make offsets and region defaults to keep classics behaviour

[StRigaud]

Buffer read, and write should now be manipulated using clEnqueue_op_BufferRect() if buffer is 2d or 3d.
CUDA version should rely on CUDA_MEMCPY for 2d and 3d.

From this we can enable a read_region and write_region method to the array class which should take the host_ptr (as source or destination). a starting coord (x,y,z) and a region size (w,h,d).

This can be mimic with the crop and paste kernel but in a less efficient way

[StRigaud]

done with

• Subregion-io #187
• Add sub-region memory copy #191

Now, read, write, copy can take an origin and a region.