Make the structure of the ESC/POS commands less opaque

(The commands are intended to be readable by people who grew up with ANSI
 escape codes so represent them that way in the code)
Actually use the barcode height and width parameters

(And reverse their order in the method signature so corrections to the
range checks don't break existing code)
Make BarcodeSizeError and BarcodeTypeError display the erroneous value

(MUCH more helpful for debugging)
Accept "CODABAR" as an alias for "NW7" in barcode()
Add the setup.py-produced "build" folder to .gitignore
Allow bypassing the resizing and height-cropping steps in fullimage()