Add some minor improvements of the package, and use temp files for the
source difference patch, such that it is more reliable. This follows
from the suggestions of @infinisil.
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
All other functions are in the form of `*{c,C}heckpointBuild*`, so we
deprecate the `mkCheckpointedBuild` function in favor of `mkCheckpointBuild`.
Also address some inconsistencies in the docs: some `buildOutput` should
actually be `incrementalBuildArtifacts`.
