Daniel J. Bernstein's redo idea is a system for building target
files from source files.  Its purpose is to provide a build system
for software packages that does incremental builds, i.e. if the
package is built and then some of its source files are changed, the
build system will only rerun that part of the build procedure that
is necessary to rebuild the changed parts of the package.

This is the redo implementation by Jonathan de Boyne Pollard written
in C++.  It comprises:

- redo - the main utility for rebuilding
- redo-ifchange - a secondary utility for rebuilding targets if
  existing sources change
- redo-ifcreate - a secondary utility for rebuilding targets if
  non-existent sources manifest
- cubehash - a utility program that generates hashes of file contents
  using the same parameterization of Bernstein CubeHash as is used
  by the redo tools to check for changes to source and target files