Housekeeping things: fix clippy lints, run formatter, upgrade dependencies

[barafael]

Hi,

i came across this lib and had a look if I could use it for a project of mine. Along the way, I checked if there were low-hanging fruit and fixed them. I applied a number of refactorings from clippy (also pedantic/nursery), which I hope you like but if not, never mind - just pick the ones you want. Let me know what you think :)