Exneus.decode

#### Is your feature request related to a problem?

`ExAws` expects that its' decoder have a `decode` function that returns `{:ok, term} | {:error, term}`

#### Describe the feature you'd like

It would be nice to have a non-raising version of `Exneus.decode!`

#### Describe alternatives you've considered

I could write my own wrapper, but this seems like a reasonable enough request

