Access to source image object

[mtking2]

This PR exposes the source Img2Zpl::Image object and all of the functionality that comes along with it provided by the img2zpl gem (and in turn all the functionality of the MiniMagick::Image class from the minimagick gem)

Usage

image = Zebra::Zpl::Image.new path: 'path/to/file.png', position: [0, 0]
image.source #=> Img2Zpl::Image instance

# also aliased as .src
image.src

Example

Flattening an image's layers (so it is properly converted) and then trimming out unnecessary white space around the edges:

label = Zebra::Zpl::Label.new width: 600, length: 305, print_speed: 6

image = Zebra::Zpl::Image.new path: 'path/to/file.png', position: [0, 0]

image.src.flatten
image.src.trim

label << image

zpl = ''
label.dump_contents zpl
puts zpl