mfs: meta issue for future refactors

From what I can tell given prior issues and PRs in go-mfs it seems like this package is due for a larger refactor rather than smaller changes.

Some issues for historical context for when someone is interested in refactoring (or writing an alternative) to mfs.
- Interface
- https://github.com/ipfs/go-mfs/issues/3
- https://github.com/ipfs/go-mfs/issues/20
- https://github.com/ipfs/go-mfs/issues/22
- https://github.com/ipfs/go-mfs/issues/31
- https://github.com/ipfs/go-mfs/issues/33
- https://github.com/ipfs/go-mfs/issues/37
- https://github.com/ipfs/go-mfs/issues/40
- https://github.com/ipfs/go-mfs/issues/54

- Bug/Feature
- https://github.com/ipfs/go-mfs/issues/4
- https://github.com/ipfs/go-mfs/issues/18
- https://github.com/ipfs/go-mfs/issues/34
- https://github.com/ipfs/go-mfs/issues/83

If someone wants a particular issue transferred here just comment, however these issues are largely historical at this point and future refactors/rewrites may go in different directions which are also fine to discuss here 😄