Convert most tutorial assets to WEBP

[damusss]

Starting from: #3362 (comment), #3362

I converted almost all tutorial assets to lossless WEBP using ffmpeg. Here are the details:

TOTAL SAVED BYTES: 429970

(1.47MB->1.06MB)

Not converted: Every jpg file (webp is larger), AdvancedInputOutput5.gif (webp was a few bytes larger)

Original File	Original Size (bytes)	New Size (bytes)	Saved Bytes
AdvancedInputOutput1.gif	5649	2690	-2959
AdvancedInputOutput2.gif	72233	64812	-7421
AdvancedInputOutput3.gif	6294	2354	-3940
AdvancedInputOutput4.gif	29185	27158	-2027
AdvancedOutputAlpha1.gif	14915	5690	-9225
AdvancedOutputAlpha2.gif	71819	65024	-6795
AdvancedOutputAlpha3.gif	30380	25066	-5314
AdvancedOutputProcess1.gif	15951	6824	-9127
AdvancedOutputProcess2.gif	1868	622	-1246
AdvancedOutputProcess3.gif	1912	626	-1286
AdvancedOutputProcess4.gif	14500	6140	-8360
AdvancedOutputProcess5.gif	16896	15766	-1130
AdvancedOutputProcess6.gif	34058	31288	-2770
Bagic-INPUT-resultscreen.png	5973	3724	-2249
Bagic-INPUT-sourcecode.png	77061	32280	-44781
Bagic-ouput-result-screen.png	4819	2908	-1911
Bagic-PROCESS-resultscreen.png	5348	3194	-2154
Bagic-PROCESS-sourcecode.png	66070	27278	-38792
Basic-ouput-sourcecode.png	57466	25636	-31830
chimpshot.gif	46010	28298	-17712
introduction-Battleship.png	165586	110422	-55164
introduction-PuyoPuyo.png	31388	18040	-13348
introduction-TPS.png	136031	95120	-40911
intro_ball.gif	5015	3588	-1427
premultiplied_alpha_composition.png	10491	4524	-5967
straight_alpha_composition.png	10119	4270	-5849
surfarray.png	50836	38938	-11898
surfarray_allblack.png	125	42	-83
surfarray_flipped.png	50835	38804	-12031
surfarray_redimg.png	23443	15926	-7517
surfarray_rgbarray.png	50897	38938	-11959
surfarray_scaledown.png	15109	12840	-2269
surfarray_scaleup.png	67759	47414	-20345
surfarray_soften.png	47540	34530	-13010
surfarray_striped.png	392	52	-340
surfarray_xfade.png	41834	30274	-11560
tom_basic.png	5139	4522	-617
tom_event-flowchart.png	5528	2670	-2858
tom_formulae.png	6763	2626	-4137
tom_radians.png	17409	9758	-7651

[Matiiss]

What about jpeg vs lossy webp? If lossy webp files are smaller, then I suppose the only concern might be the resulting quality after converting an already lossy format to another lossy format, but maybe it's fine.

[Starbuck5]

I see a saving of 314 kb, nice!

[ankith26]

LGTM, thanks for the PR 👍