Migrate to GitHub Actions

Travis is dead (sort of), so we move to GitHub Actions.

Bintray is also dead, so we are just storing packages as build
artifacts.

This also removes the dependency (as a git submodule) to beaver. Under
the current circumstances beaver provides very low value.

Author: llucax

.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: CI
+on: [create, pull_request, push]
+jobs:
+  CI:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0  # Needed to make sure to proper git describe
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install python3 python-docutils ruby-dev
+          sudo gem install fpm
+      - name: Build
+        run: make PYTHON=python3 all deb
+      - name: Archive package artifacts
+        uses: actions/upload-artifact@v2
+        with:
+          name: deb
+          path: deb/git-hub_*.deb
+          if-no-files-found: error