Add supp. mat. functionality

[tpoisot]

This led to a significant change in how the manuscript are built, with the built steps being done by https://github.com/PoisotLab/manuscript-typesetter/ -- this is installed by the GitHub action, and referred to by release number.

• Closes #5

• Closes #18

• [x] find a way to specify supp mat

• [x] decide on headers for the supp mat

• [x] find a way to build supp mat

• [x] find a way to report supp mat in the html page

• [x] bundle the supp mat to the pdfs

[github-actions[bot]]

Current word count (main text; no references) is approx. 1540

[tpoisot]

Maybe use https://github.com/marketplace/actions/combine-pdfs ?

[github-actions[bot]]

Current word count (main text; no references) is approx. 2107

[github-actions[bot]]

Current word count (main text; no references) is approx. 2107

[github-actions[bot]]

Current word count (main text; no references) is approx. 2107

[github-actions[bot]]

Current word count (main text; no references) is approx. 1734

[github-actions[bot]]

Current word count (main text; no references) is approx. 1766