Update Dockerfile, copy everything, use makefile

I have figured out the `.dockerignore` file so I don't have to do manual
context size management like before.

The Dockerfile now uses the Makefile to ensure image builds contain the
same thing non-image builds would.

Dockerfile

@@ -5,18 +5,9 @@ RUN apt-get install -y --no-install-recommends libasound2-dev libudev-dev
 RUN rustup target add wasm32-unknown-unknown
 RUN cargo install --locked wasm-bindgen-cli
 
-# Copy in only the parts we care about. This is to prevent Docker from re-
-# running some steps because unimportant files changed (e.g.: the .git/ folder)
-COPY src/ ./src
-COPY Cargo.toml ./Cargo.toml
-# WARN: The lockfile doesn't exist in the repo. You will have to create it
-# before building the Docker image (i.e.: run `cargo update` first)
-COPY Cargo.lock ./Cargo.lock
-COPY www/ ./www
-COPY Makefile ./Makefile
+COPY . .
 
-# Oops. There's no text output in the Docker build command line (it still works, though)
-RUN make
+RUN make -j
 
 FROM busybox:musl
 RUN mkdir -p /var/www