Change stack from `failure` to `std::error::Error`

[bltavares]

Feature Request

Summary

Nowadays hypercore is defined for storage where errors are failure::Error eg

This predates when Rust had std::error::Error trait, and could now be replaced with a Error + Send + Sync + 'static, such as anyhow, snafu or coreerror for a no_std crate.

This is also one less crate on the stack.

Motivation

This should help us move into no_std in the future, specially useful for WASM and embedded.

Guide-level explanation

We could replace failure with anyhow on random-access-disk and random-access-storage to use context during errors, which is also compatible with std::error::Error.

We can then define hypercore using the std Error trait, and broaden the types of Storages hypercore can use.

Reference-level explanation

Drawbacks

• Increase min rust version (would be increased by Async API on hypercore #97 anyway)

Rationale and alternatives

Unresolved Questions

[bltavares]

PRs with moves opened and linked to the issue.