Fix missing manual cross-references to guide-build#159

Merged

rptb1 merged 7 commits intomasterfrom

branch/2023-02-16/manual-xrefs

Feb 23, 2023

Commits on Feb 16, 2023

Commits on Feb 19, 2023

Adding note to manual/build.txt to prevent manual breakage.
rptb1
committed

Commits on Feb 22, 2023

Make Sphinx fail on warnings so that CI detects problems with the manual early <https://github.com/Ravenbrook/mps/issues/158#issuecomment-1440828613>. Fixing warnings. Undoing mystery merge <http…
rptb1
committed

Commits on Feb 23, 2023