add DigitalSource::Get so DigitalSource is actually usable

This is our wpilib commit 1e9a531ce33128440fc9030a5a852bc8bbf65b91 and
still uses FPGA image v23.

This also includes adding 2 files I missed in previous wpilib changes.

Change-Id: Ief3ce091c600c290129c9ac8f66cdb0766d23df1
7 files changed
tree: 6e2f48a9ef24eb2539358c9d5775225212ef9410
  1. aos/
  2. doc/
  3. frc971/
  4. output/
  5. vision/
  6. .clang-format
  7. .gitignore
  8. README.txt