Avoid some compiler complaints about unused variable

Clean up curses formatting

Actually fix the normalization and zero-divisor issue

Properly detect and protect against zero divisors

Compute and display the pct. contribution of each PID gain to the output

Add more sensible defaults to pid_gains constructor

Remove unnecessary std::ostream << std::chrono::time_point<...>

Clean up default output respresentation for units::value

Merge branch 'feature-pid'; v2.2.0

Add an ezpwd/pid demo to README

Use c++/ezpwd/units for units management in pid-test.C

Fix some warnings

Add PID loop ezpwd/pid, as well as ezpwd/{units,cut}

Merge branch 'feature-nix'

Integrate nix-build supplied c/c++ include/library paths into build