Align input buffers before reading or writing inotify events

[FenrirWolf]

Attempts to solve #155

This passes the current tests and eliminates the miri warning about unaligned references that currently triggers here, but I'm not certain if it's fully robust. The alignment code works by splitting away any unaligned portion of the input buffer, and so I'm not sure if the byte-tracking code in Stream and other places needs to be updated to reflect that.

[hannobraun]

Thank you for the contribution, @FenrirWolf!

This looks good. My only concern is whether other parts of the library need to be updated, as you mention. I will take a closer look next week.

[hannobraun]

I've checked the rest of the code, and I think everything's fine. The stream code uses the same core primitives that this PR updates (Event::from_buffer, read_into_buffer), so I think it's fully covered by this fix.

What I don't like about this fix is how subtle it is. The alignment needs to be considered in multiple places, and while I think this PR gets it right, future changes might mess it up again. Still, I think this PR fixes the unsoundness, so I'm going to merge it.

I think it would be better, if we could somehow use a custom buffer type to enforce the alignment at the type level. I'm not sure how practical that is, and I don't have the bandwidth to look into that. If anyone wants to look into that approach, that would be very welcome.

Thanks again, @FenrirWolf!