Added clang-format linter (aws#71)

* Added clang-format linter

* Fixed cJSON

Author: Justin Boswell

.github/workflows/clang-format.yml

@@ -0,0 +1,19 @@
+name: Lint
+
+on: [push]
+
+jobs:
+  clang-format:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout Sources
+      uses: actions/checkout@v1
+      
+    - name: clang-format lint
+      uses: DoozyX/[email protected]
+      with:
+        # List of extensions to check
+        extensions: c,h
+        exclude: './include/aws/crt/external/cJSON.h'