Release v0.1.1

Added

• Docker build scripts (docker/erlang, docker/elixir) and READMEs for
  building the lambda-layer-erlang and lambda-layer-elixir images that
  mix aws_lambda.build pulls from.
• mix aws_lambda.build — --dep/-d flag to install extra dnf packages
  (e.g. git) in the build container alongside tar.

Changed

• mix aws_lambda.build — colorized, more consistent step output; internal
  cleanup.

Removed

• AWS.Lambda.Runtime.MixRelease (priv/mix/release.exs) — the release
  steps it configured are documented directly in the README instead.