Consider using Snafu to define Error types

[alxiong]

As a follow-up of #84 where we remove Snafu on jf-utils's TaggedBlobError temporarily.

We aim to try to use Snafu among all jf-* crates and enabled for all the error types we defined and we internally depend on (such as TBase64Error etc)

cc @jbearer

[ggutoski]

Jeb and I briefly discussed enforcing a library-wide anyhow-only policy. Anyhow is far more ergonomic when it's used everywhere. Otherwise there's a constant need for boilerplate code to translate among error types and cruft at every ?.