Implement asynchronously reading TDMS files using tokio::fs

[mettekou]

Asynchronously reading large TDMS files using tokio::fs could be beneficial for performance. I am willing to create a pull request for this and draw on my experience from implementing reading TDMS files in F#.

[DnOberon]

I'm all for it! I don't spend as much time on this library as I'd like, between my day job etc. so any and all help is awesome. I wrote this before I actually became familiar with async/await and tokio at all - so there absolutely can be some changes here.