@posts/OuroborosSinCos.md; improves

Is similar to: commit 450066f (@`posts/OuroborosSinCos.md`; `remark-lint` fixes:). TODO: group this with thus
@`./posts/OuroborosSinCos.md`;
	@`#discussion`: *Fourier-transform* discussion moved to `#discussion-2`. `#iscussion` now just discusses `sin` & `cos` & sims.
		+`posts/images/3D_Spherical.svg`
	+`#discussion-2`: includes the old *Fourier-transform* discussion, plus followup question of how to use *Fourier-transform* on `sin` / `cos`.
		+`posts/images/Laplace's_equation_on_an_annulus.jpg`
	Extra whitespaces in code blocks (`` ``` ... ``` ``) removed.
	`:%s/^    /> /`: replaces block code with block quotes.
		`:%s/\[\([0-9,. ]\+\)\]/`\0`/`: just used for rows which got *Markdown* errors such as "warning Unexpected reference to undefined definition, expected corresponding definition (`-0.4161, 0.9093`)" from the switch to block quotes.

Author: SwuduSusuwu