doxygen generation fails when the github repository is private

[produino]

This is common during initial development for a library but the current script (doxy_gen_and_deploy.sh) assumes that the github repository is public, and only applies the GH_REPO_TOKEN when commiting the changes back to the branch missing it on the initial checkout which causes the following error:
fatal: could not read Username for 'https://github.com': No such device or address ##[error]Process completed with exit code 128.

[ladyada]

hi you can submit a PR fix, we only have public repos