initial circle-ci configuration (#4807)

circle.yml

+machine:
+  services:
+    - docker
+
+checkout:
+  post:
+    - git submodule sync
+    - git submodule update --init --recursive
+
+## Customize dependencies
+dependencies:
+  pre:
+    - docker pull px4io/px4-dev-base
+    - docker info
+
+test:
+  override:
+    #- sudo docker run --rm -v `pwd`:`pwd`:rw -v $HOME/.ccache:$HOME/.ccache:rw -e CCACHE_DIR=$HOME/.ccache -w=`pwd` --user=$UID -it px4io/px4-dev-base /bin/bash -c "make"
+    - docker run -v `pwd`:`pwd`:rw -w=`pwd` --user=$UID -it px4io/px4-dev-base /bin/bash -c "make"