Reading files quickly in Rust

Simple file I/O is such a great task to blog about as there's a long evolution of 'discovery' permitted:

1. oh wow, syscalls are really slow. We need to get as much done as we can with as few of these as possible

2. that's kind of annoying though, what if we had ... some kind of ... transparently buffered ... interface?

3. woah that buffered I/O thing I discovered last time, I just found out that my C programs have been using that this whole time! what cheaters!

4. hmm, even though I have 9000 CPUs each trying to process I/O from this single filesystem, I'm not getting the 9000x speedup I would expect. wait, wait. I just had a thought. try and keep up with me here. Filesystems must exist somewhere in reality, right? On some part of my macbook? What part is that?

5. oh wow spinning disks have really weird performance characteristics

6. oh wow it's enormously faster to read serial data even in RAM! Even though it has 'random-access' right in the name, random access is slower! This is going to be an epic-length blog series guys! We're rediscovering everything!