Merge branch 'gitlab-ci' into 'master'

add .gitlab-ci.yml

See merge request reform/reform!41

.gitlab-ci.yml

+image: debian:unstable-slim
+
+build:
+  artifacts:
+    paths:
+      - reform2-keyboard-fw/keyboard.hex
+      - reform2-trackball-fw/Mouse.hex
+      - reform2-trackpad-fw/Mouse.hex
+      - reform2-lpc-fw/bin/firmware.bin
+  script: |
+    apt update
+    apt-get --no-install-recommends -y install build-essential avr-libc gcc-avr gcc-arm-none-eabi libnewlib-arm-none-eabi
+    make -C reform2-keyboard-fw
+    make -C reform2-trackball-fw
+    make -C reform2-trackpad-fw
+    make -C reform2-lpc-fw lpcrc
+    make -C reform2-lpc-fw