[ImgBot] Optimize images

*Total -- 71.81kb -> 60.25kb (16.1%)

/overview.dot.svg -- 3.18kb -> 2.44kb (23.33%)
/dox/opti_4.svg -- 2.67kb -> 2.10kb (21.26%)
/dox/libfoo.svg -- 3.19kb -> 2.57kb (19.63%)
/dox/opti_2.svg -- 4.42kb -> 3.65kb (17.36%)
/dox/opti_5.svg -- 10.40kb -> 8.73kb (16.1%)
/dox/opti_2b.svg -- 6.61kb -> 5.57kb (15.66%)
/dox/opti_6.svg -- 10.00kb -> 8.50kb (15.02%)
/dox/opti_3.svg -- 10.41kb -> 8.85kb (14.98%)
/dox/opti_1.svg -- 8.82kb -> 7.52kb (14.75%)
/dox/optimizer.svg -- 12.12kb -> 10.33kb (14.73%)

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