Add support for -relation-created hook (#601)

Copy the hook template in for -relation-created hooks so that they are
handled by the charm.

Also switch to GitHub Actions for tests instead of Travis.

.github/workflows/tox.yaml

@@ -0,0 +1,20 @@
+name: Test Suite
+
+on:
+  - pull_request
+
+jobs:
+  tox:
+    name: Tests
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out code
+      uses: actions/checkout@v2
+    - name: Setup Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.7
+    - name: Install Tox
+      run: pip install tox
+    - name: Run tests
+      run: tox

charmtools/build/tactics.py

@@ -515,6 +515,7 @@ class InterfaceBind(DynamicHookBind):
     relation hooks needed by this charm.
     """
     HOOKS = [
+        '{}-relation-created',
         '{}-relation-joined',
         '{}-relation-changed',
         '{}-relation-broken',