Ingore cover_db/ directory.
Video::Delay::Array: Add tests.
Video::Delay::Const: Add tests.
Video::Delay::Func: Improve error message.
Video::Delay::Func: Add tests.
Video::Delay::Func: Add callback for 'func' parameter.
Video::Delay::Func: Add EXAMPLE section to doc.
Video::Delay::Func: Add error check for 'func' parameter.
Rewrite default value of 'func' to subroutine reference.
Remove TODO.