`Timer`: Remove `periodic()` and `timeout()`

[llucax]

The names are just too confusing and we'll never find a name that can convey all the intricacies of timers in the async world, so it is better to just remove periodic() and timeout() and force users to pass the missing ticks policies manually.

Fixes #253.

[shsms]

Although not strictly necessary, in this case it is easy to make all commits pass CI by just moving the first commit to near the end.

[llucax]

Although not strictly necessary, in this case it is easy to make all commits pass CI by just moving the first commit to near the end.

True, but I thought review-wise It makes more sense to start with the important change first, and then adapt the code to deal with that change. I'm trying to prioritize easy of review when splitting the commits.

I can move the commit if you prefer though...

[llucax]

Updated to fix the typo and move the removal from the code to the end.

[llucax]

Enabled auto-merging.