[ImgBot] Optimize images (#15)

*Total -- 608.98kb -> 491.61kb (19.27%)

/images/03-table3_1.png -- 12.89kb -> 7.72kb (40.15%)
/images/04-fig4_14.png -- 73.83kb -> 44.55kb (39.65%)
/images/04-fig4_3.png -- 23.16kb -> 14.41kb (37.8%)
/images/04-fig4_13.png -- 21.18kb -> 13.75kb (35.11%)
/images/04-fig4_12.png -- 20.45kb -> 15.45kb (24.48%)
/images/03-fig3_4.png -- 48.49kb -> 36.95kb (23.8%)
/images/04-fig4_11.png -- 19.21kb -> 14.75kb (23.24%)
/images/03-fig3_12.png -- 26.42kb -> 21.66kb (18.04%)
/images/03-fig3_9.png -- 55.48kb -> 46.86kb (15.54%)
/images/03-fig3_16.png -- 174.95kb -> 148.23kb (15.27%)
/images/04-fig4_2.png -- 18.22kb -> 16.37kb (10.14%)
/images/03-95-percent-confidence-interval.jpg -- 114.68kb -> 110.93kb (3.27%)

Signed-off-by: ImgBotApp <[email protected]>
Co-authored-by: ImgBotApp <[email protected]>
Co-authored-by: Jon Harmon <[email protected]>

Author: 3 people