Tracking issue for v0.2

Now that we have maintainers for this crate I think it's about time there were fixes to long standing issues like #20. It's probably worth making this a breaking update to avoid any issues with unmaintained users of the current version (and would be a good opportunity to make other breaking changes if there are any).

Checklist of things to sort out before releasing 0.2.0 (feel free to add more items and pull these out to separate issues if they need discussion):

- [ ] Issues:
- [x] #20 (PR #21)
- [ ] #16
- [x] #29 (PR #31)
- [ ] #30
- [ ] #34
- [ ] Sort out licensing (#19 + the repo is missing license files for the current license, PR #32).
- [x] rustfmt + clippy (PR #27)
- [x] Update travis config (rustfmt + clippy, stable + beta + nightly, minimum Rust version) (PR #33)
- [x] Update metadata (at a minimum links + authors in `Cargo.toml`, PR #37)
- [ ] Improve documentation
- [x] Update to 2018 edition (PR #38)