adding github ci

.github/workflows/ci.yml

@@ -0,0 +1,19 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        nim: [stable, 1.6.18, 1.4.8, 1.2.18]
+    steps:
+    - uses: actions/checkout@v2
+    - uses: iffy/install-nim@v3
+      with:
+        version: ${{ matrix.nim }}
+    - name: Build
+      run: nimble install -y
+    - name: Test
+      run: nimble test -y