Enable Gitlab CI builds (#1)

Currently only builds for BOARD=devboard and uploads the bin and elf files.

.gitlab-ci.yml

@@ -0,0 +1,15 @@
+image: registry.gitlab.maxregan.me/max/arm-build-image:latest
+
+build:
+  stage: build
+  variables:
+    BOARD: "devboard"
+    GIT_SUBMODULE_STRATEGY: "recursive"
+  script:
+    - make -C ./firmware/
+  artifacts:
+    paths:
+      - "firmware/Test/*.elf"
+      - "firmware/Test/*.bin"
+      - "firmware/Application/*.elf"
+      - "firmware/Application/*.bin"