Removed support for timerfd on Android as it seems to have been deprecated? See https://android.googlesource.com/platform/development/+/73a5a3b/ndk/platforms/android-20/include/sys/timerfd.h or https://github.com/rust-lang/libc/issues/1589
Removed the public status of `TimerSpec`, as it should not be exposed to the user.
Implemented `FromRawFd` for `TimerFd` as it already implements `AsRawFd`.
Addressed comments from the latest code review:
- Removed upper bound assertions on timer expirations in tests.
- Made the main example runnable and added code to show how to wait for the timer.
- Refactored `ClockId` to use `libc_enum`.
- Added comments for all public parts of the module.
- Wrapped to 80 cols.
- Changed the size of the buffer in the tests to the minimum required.
* Ran rustfmt.
* Added a `From` implementation for `libc::timespec` -> `TimeSpec`.
* Reworked the example with the new changes and changed the timer from 5 to 1 second.
* Added a constructor for a 0-initialized `TimerSpec`.
* Added a new method to get the timer configured expiration (based on timerfd_gettime).
* Added an helper method to unset the expiration of the timer.
* Added a `wait` method to actually read from the timer.
* Renamed `settime` into just `set`.
* Refactored the tests and added a new one that tests both the `unset` and the `get` method.
Modified CHANGELOG.
