deny warnings and unsafe code in tests and examples

examples/full-syntax.rs

examples/generics.rs

examples/late-resources.rs

examples/nested.rs

examples/one-task.rs

examples/preemption.rs

examples/two-tasks.rs

examples/zero-tasks.rs

tests/cfail/critical-section.rs

tests/cfail/duplicated-task.rs

tests/cfail/exception.rs

tests/cfail/idle.rs

tests/cfail/init.rs

tests/cfail/interrupt.rs

tests/cfail/late-resource-init.rs

tests/cfail/lock.rs

tests/cfail/peripheral-alias.rs

tests/cfail/priority-too-high.rs

tests/cfail/priority-too-low.rs

tests/cfail/resource-alias.rs