Implement block aperture (AB)

[abetusk]

Section 4.6 of rev. 2017.11 of The Gerber Format Specification.

Block apertures can be nested and reference other aperture definitions.

example:

G04 Ucamco copyright*
%TF.GenerationSoftware,Ucamco,UcamX,2016.04-160425*%
%TF.CreationDate,2016-04-25T00:00;00+01:00*%
%TF.Part,Other,Testfile*%
%FSLAX46Y46*%
%MOMM*%
G04 Define standard apertures*
%ADD10C,7.500000*%
%ADD11C,15*%
%ADD12R,20X10*%
%ADD13R,10X20*%
G04 Define block aperture D100, consisting of two draws and a round dot*
%ABD100*%
D10*
X65532000Y17605375D02*
Y65865375D01*
X-3556000D01*
D11*
X-3556000Y17605375D03*
%AB*%
G04 Define block aperture D102, consisting of 2x3 flashes of D101 and 1
flash of D12*
%ABD102*%
G04 Define nested block aperture D101, consisting of 2x2 flashes of D100*
%ABD101*%
D100*
X0YD03*
X0Y70000000D03*
X100000000Y0D03*
X100000000Y70000000D03*
%AB*%
D101*
X0Y0D03*
X0Y160000000D03*
X0Y320000000D03*
X230000000Y0D03*
X230000000Y160000000D03*
X230000000Y320000000D03*
D12*
X19500000Y-10000000D03*
%AB*%
G04 Flash D13 twice outside of blocks*
D13*
X-30000000Y10000000D03*
Copyright Ucamco NV
Having a question or remark about the spec? Please contact us at gerber@ucamco.com
83X143000000Y-30000000D03*
G04 Flash block D102 3x2 times*
D102*
X0Y0D03*
X0Y520000000D03*
X500000000Y0D03*
X500000000Y520000000D03*
X1000000000Y0D03*
X1000000000Y520000000D03*
M02*

output:

[abetusk]

This is still a work in progress but the branch gerber-extensions should now support Aperture Blocks.

Before that branch gets merged into release I'd like to add the other Gerber extensions (I believe the SR and some other LP codes are the major ones yet to be implemented) as well as provide some tests.