Layered images - Githubissues

[x] Every image has a layer count (typically = 1). Uninitialized images have layer count = 0.
[x] layers() call return correct value.
[x] int layerOffsetInBytes() pure const
[x] Images with zero layer are authorized (much like images with width == 0 and height == 0) are legal
[x] actually allocate images with several layers (vertical borders for each layer, but also horizontal).
[x] LAYOUT_GAPLESS specify that layers are sticked together? or no difference.
[x] possibility to convert scanlines across all layers, convertTo works
[x] API for getting scanline of particular layer
[x] API for getting individual layer subimage
[x] API for getting range of layer subimage
[x] support createViewFromData with layers
[x] support createWithNoData withlayers
[x] convertTo should work
[x] flipVertical, flipHorizontal
[x] clone
[x] copyPixels
[x] usability: it must be width, then height, then layerCount
[x] documentation of all that

AuburnSounds / gamut