…d as RS274-X2.

Note that this is only a single image, so tracks will appear crossed since they
are possibly taken from multiple copper layers.  This will be fixed in next commit.

Also, there is currently no annotation of normal gerbers.  Only the image struct from
the IPC file has the net, refdes, pin etc. attributes.  These will need to be
matched up by coordinate location to other gerber images.

This allows visual splitting of layer info.  e.g.
  gerbv --ipcd356a-layers=0,1,2 foo.ipc foo.ipc foo.ipc --ipcd356a-tracks=y,y,y
will open foo.ipc into three distinct images, for board outline, top and bottom
layers.  Tracks are shown for all three.

Added x2 attributes to the project structure.  This is an easily expandable
way of passing arbitrary options to file readers etc.

Also added some functionality for text (label) display.  Command line
args now allow text color and font size ranges to be entered.
On zooming in, the text will change sizes within bounds so as to
maintain visibility without excessive clutter.

Command line arg --layers added to allow specifying file function
and related attributes for each RS274-X/D file read in.

This is basically a demo of the new search API.  When mouse is
near an object, its standard attributes (or label) will be shown
in the status bar, next to the selected object (if any).

Process tracks as well as pads;
Don't mix track and pad annotations;
Properly handle access=00 in IPC by passing bottom layer number.
Ignore polygon pours unless from aperture macro.

Mouse hover selection of net object will cause other objects in
the same image (layer) to be XOR highlighted if they have matching
netname or refdes.  Obviously, this needs a source of netname and
refdes information, such as IPC-D-356A.

Known issues:

XOR highlighting defeats itself if e.g. a track is generated with
an even number of overlapping strokes.  Proper solution requires
using Cairo instead of deprecated GDK API.

Also added some test cases for IPC-D-356A files.

Changed some golden PNG files to account for pixel differences.
May be because I'm on old OS level (Ubuntu 16.04).

Also added some functionality for text (label) display.  Command line
args now allow text color and font size ranges to be entered.
On zooming in, the text will change sizes within bounds so as to
maintain visibility without excessive clutter.

Command line arg --layers added to allow specifying file function
and related attributes for each RS274-X/D file read in.

This is basically a demo of the new search API.  When mouse is
near an object, its standard attributes (or label) will be shown
in the status bar, next to the selected object (if any).

Process tracks as well as pads;
Don't mix track and pad annotations;
Properly handle access=00 in IPC by passing bottom layer number.
Ignore polygon pours unless from aperture macro.

Mouse hover selection of net object will cause other objects in
the same image (layer) to be XOR highlighted if they have matching
netname or refdes.  Obviously, this needs a source of netname and
refdes information, such as IPC-D-356A.

Known issues:

XOR highlighting defeats itself if e.g. a track is generated with
an even number of overlapping strokes.  Proper solution requires
using Cairo instead of deprecated GDK API.

Also added some test cases for IPC-D-356A files.

Changed some golden PNG files to account for pixel differences.
May be because I'm on old OS level (Ubuntu 16.04).

…to ipcd356a

This adds several steps to test integrity of export/reimport:
1. Do initial image comparison to "golden" reference image.
2. Export as RS274-X
3. Import from step (2), and write as image.
4. Compare image from (1) to image in (3) - should be exact match.
5. Import from step (2), write as RS274-X.
6. Text diff output from step (2) and step (5) - should be exact match
   since after first export, the Gerber file should be in a canonical
   form.

Note that many tests fail the reimport test.  A future commit
will resolve that.