Fix frame array

The memory layout of the was assumed to be the wrong way round. It
should be [:height, :width] and as such [y,x] not [x,y].
Rename variable in frame_array
Return a memory view of video size

Returns a slice of the whole memory view of the usable memory rather
than exposing the padded bits.
Take account of subsampling in exported array

In get_read/write_array take account of the width's subsampling.
Merge pull request #117 from splinter98/pyframedata

Fix Broken Python Data Export