Add example with more math formulas

[Omikhleia]

Closes #45

Fixed the SIL file from my earlier ZIP provided in the issue, and proposed here -- I don't know if this is the right way to proceed.

[Omikhleia]

The expected result should look as follows:

(SILE v0.15.7 (LuaJIT 2.1.1731601260) [Rust])

[alerque]

Looks great, and yes this should be all there is too it to add an example to the website.

[alerque]

Suggested change

	fn = "math-formulas"
	fn = "math-formulas"
	devel = true

I don't know if you need this change, but if you even need an example to build with the current default development branch (currently master) then you can add this flag.

$ nix-shell --run 'sile --version'
SILE v0.15.7 (LuaJIT 2.1.1713773202) [Rust]

Ergo if you need anything in v0.15.8 or later, add this flag. Otherwise it will build the example with v0.15.7.

[alerque]

I think the CI failure is unrelated to this PR. I'll look into it.

[alerque]

CI failure is because we broke the Lua API documentation build in v0.15.7 (which is why that version's blog post never went online). This CI failure is just a cascade of that failure.

[Omikhleia]

we broke the Lua API documentation build in v0.15.7

Not sure it's related, but I've noted (my bad) some typing errors in the CSL support. 'Was about to go for a fix.