add CI

.gitlab-ci.yml

+image: "rust:latest"
+
+stages:
+  - lint
+  - build
+
+before_script:
+  - rustup target add wasm32-unknown-unknown
+  - rustup component add rustfmt
+  - rustup component add clippy
+
+lint:
+  stage: lint
+  script:
+    - cargo fmt -- --check
+    - cargo clippy --all-features -- -D warnings
+
+build:
+  stage: build
+  script:
+    - cargo build --release
+    - make
+    - cargo run --release -- --out out.gif
+  artifacts:
+    paths:
+      - out.gif
+      - target/rapidriter-cat.wat