Added Circle CI configuration

Necessary to switch over to Circle CI for this in order to be consistent with how we build both the TRMNL i18n and TRMNL API gems.

Milestone: minor

.circleci/config.yml

@@ -0,0 +1,36 @@
+version: 2.1
+jobs:
+  build:
+    working_directory: ~/project
+    docker:
+      - image: bkuhlmann/alpine-ruby:latest
+    steps:
+      - checkout
+
+      - restore_cache:
+          name: Gems Restore
+          keys:
+            - gem-cache-{{.Branch}}-{{checksum "Gemfile"}}-{{checksum "trmnl-liquid.gemspec"}}
+            - gem-cache-
+
+      - run:
+          name: Gems Install
+          command: |
+            gem update --system
+            bundle config set path "vendor/bundle"
+            bundle install
+
+      - save_cache:
+          name: Gems Store
+          key: gem-cache-{{.Branch}}-{{checksum "Gemfile"}}-{{checksum "trmnl-liquid.gemspec"}}
+          paths:
+            - vendor/bundle
+
+      - run:
+          name: Build
+          command: bin/rake
+
+      - store_artifacts:
+          name: SimpleCov Archive
+          path: ~/project/coverage
+          destination: coverage