Build side docker container to use in multistage builds for reducing total container size

• Source repo bbc/audiowaveform
• This repo is alpine Dockerfile with audiowaveform building in it
• Docker Hub Container with builded audiowaveform binaries. (audiowaveform and audiowaveform_test are in /bin directory)

Link container and copy binaries from it. Don't forget about required libraries.

FROM genesix/docker-audiowaveform-alpine:latest as audiowaveform-builder

FROM alpine:3.9

RUN apk add --no-cache libmad libsndfile libid3tag gd boost boost-program_options

COPY --from=audiowaveform-builder /bin/audiowaveform /usr/local/bin