Four of the five physics crates are done, 104 of 239 blocks in the layer.
The remaining one is apsis-frames, which holds the IAU 2000 Earth
orientation models and carries the largest number of formulas.
Running rustdoc with -D warnings found nine broken links: a misspelt
WGS84, links to methods and constants that are private or in a crate that
is not a dependency, and three redundant explicit targets. Fix each and add
a documentation step to CI so a doc comment cannot drift away from the code
it describes without the build noticing.
ApsisRS contributors