verbatim copies of image.gjdens and projection arguments
verbatim copy of flip.array and friends
fix up flip methods

* inc help and exports
* though why I need the @rdname directive for the flip.array method beats me
test flip methods for matrices/arrays
preliminary version of imslice to slice out subarray

* works ok, except for bounding box problems with singleton dimensions
remove unused (and undocumented) ... argument in imslice
Basic implementation of projection function
export imslice
Basic implementation of image.im3d
fix construction of im3d objects from 2d data
don't check attributes of imslice return value for time being

* we would like to check some _matching_ attributes
update family directives
define all.equal.im3d testing only key attributes
New function to define the origin of an im3d object
all.equal.im3d should check dim attributes when present
New function to set the boundingbox of an im3d object

* and tests
Additional tests for imslice +/- drop argument
Set projected dimension to have BoundingBox 0

* think about whether this should be 0 or NA or midpoint of original (FIXME)
test that we can set the boundingbox to NULL
test that we can make a sum projection in z