Feature request: Configurable typesetting engine (like xelatex or lualatex)

[joshuahhh]

When I try to use Living Papers with the PLATEAU LaTeX class, LaTeX tells me:

! Fatal Package fontspec Error: The fontspec package requires either XeTeX or
(fontspec)                      LuaTeX.
(fontspec)
(fontspec)                      You must change your typesetting engine to,
(fontspec)                      e.g., "xelatex" or "lualatex" instead of
(fontspec)                      "latex" or "pdflatex".

Switching from pdflatex to xelatex in the LP code seems to fix things. Would be great to have this as an option, if that doesn't open too many cans containing too many worms.

[joshuahhh]

Random note for posterity: The PLATEAU LaTeX class also relies upon biber as a BibTeX backend, and biber doesn't like citation keys with parentheses in them, making this the hilarious flip side to #23.