Add a better Docker build script + update Dockerfile (#4222)

* Add a Docker build script

* Add usage and error messages

* Add -r to reads

Thanks mechmerlin

* Add keyboard:keymap form, improve script

* Add target argument, change usage forms in script

* Add check for more than 3 args in keyboard:keymap:target form

* Change Docker base image to debian, use community repo

This matches what qmk_compiler uses (https://github.com/qmk/qmk_compiler/blob/master/Dockerfile#L1).

I've removed the maintainer as we now have a community build on Docker Hub (https://hub.docker.com/r/qmkfm/qmk_firmware). This Dockerfile will also be maintained by the community.

* Change build command format to keyboard:keymap

* Call make directly in container run command

* Simplify script, remove 3-arg form

* Add COPY to Dockerfile so images are usable in and of themselves

Also change WORKDIR from /qmk to /qmk_firmware

* Add USB pass-through for Linux and docker-machine hosts

* Read directly into variables instead of array

* Alphabetically sort dependencies in Dockerfile

* Set executable bit on util/docker_build.sh

* Update Docker docs

* Add warning about Docker on Windows

* Expand comment in docs

* Check docker-machine exit code instead of string

* Only match --help with whole arguments

* Make script POSIX-compliant

* Convert script indentation to tabs

Dockerfile

@@ -1,28 +1,29 @@
-FROM debian:jessie
-MAINTAINER Erik Dasque <erik@frenchguys.com>
+FROM debian
 
-RUN apt-get update && apt-get install --no-install-recommends -y build-essential \
+RUN apt-get update && apt-get install --no-install-recommends -y \
+    avr-libc \
+    avrdude \
+    binutils-arm-none-eabi \
+    binutils-avr \
+    build-essential \
+    dfu-programmer \
+    dfu-util \
     gcc \
+    gcc-arm-none-eabi \
+    gcc-avr \
+    git \
+    libnewlib-arm-none-eabi \
+    software-properties-common \
     unzip \
     wget \
     zip \
-    gcc-avr \
-    binutils-avr \
-    avr-libc \
-    dfu-programmer \
-    dfu-util \
-    gcc-arm-none-eabi \
-    binutils-arm-none-eabi \
-    libnewlib-arm-none-eabi \
-    git \
-    software-properties-common \
-    avrdude \
     && rm -rf /var/lib/apt/lists/*
 
-ENV keyboard=ergodox
-ENV subproject=ez
-ENV keymap=default
+ENV KEYBOARD=ergodox_ez
+ENV KEYMAP=default
 
-VOLUME /qmk
-WORKDIR /qmk
-CMD make clean ; make keyboard=${keyboard} subproject=${subproject} keymap=${keymap}
+VOLUME /qmk_firmware
+WORKDIR /qmk_firmware
+COPY . .
+
+CMD make $KEYBOARD:$KEYMAP