Improve makefile documentation
Remove unused makecheck.py --difftest mode
Fix typo
Add Target.build_complete() to allow for post-build processing
Support I/O communication with job processes via new class ExternalPipedCommandJob
Use weakref instead of slow and unintuitive Make.get_target_by_file_path()
Avoid intricated code in Target-derived classes’ constructors
Allow Target.build_complete() to alter the job’s return code
Move comparison in ComparisonUnitTestTarget to Target.build_complete() override

Working toward merger of ComparisonUnitTestTarget and
ComparisonUnitTestTarget, to allow comparing just about anything:
•  unit test output
•  preprocessor output
•  external files