Make typsium work for nuclear reactions

[gvdeynde]

Hi

Currently, typsium parses a string for the element/isotope assuming the element name starts at least with a capital Roman letter and might be followed by a second but non-capital Roman letter:

typsium/src/parse-formula-intermediate-representation.typ

Line 16 in 5b66e70

"([A-Z][a-z]?)" +

Could it be modifed to accept also single non-capital Roman letters or even Greek letters? This would allow me to write a neutron capture reaction on U238 like

ce("^238_92U + ^1_0n -> ^239_92U")

or another particle interaction like

ce("^10_5B + ^4_2α -> ^13_6C + ^1_1H")

I think it would sufffice to change the regexp to
"([A-Za-zα-ωΑ-Ω][A-Za-z]?)"

Would it break something else?