C++ flavored datacheck.sh

[yakra]

If we're to eventually switch to the C++ version of the site update program, it makes sense to also implement a C++ flavored datacheck.sh. The first few thoughts that come to my head:

• how many threads to run, once we have threads
• make included as part of datacheck.sh
  • special build to limit number of threads allowable?
• include git pull as part of datacheck.sh itself, or continue to input that manually as specified in RUNNING.md?
• [x] chmod +x datacheck.sh?
  • sh datacheck.sh -> ./datacheck.sh?
• [x] some more options here (existing file too): https://github.com/TravelMapping/DataProcessing/blob/6e98c786abf729bf195473d9a9a4d0171f2e8c82/siteupdate/python-teresco/datacheck.sh#L10-L15

[yakra]

Future: turn off Makefile echoing for the executables themselves