Let make recurse into subdirectories
Finish X7.2
Finish X.7.6
Finish X.7.7
Introduce OUTPUTDIR, to separate sources from built files.
Finish X.7.8
Finish X.7.8
Add gtest, finish X.8.7 and X.8.8.
Put gtest makefile bits in a separate include file.
Finished X.8.8