Move to Swift Package Manager disregarding Cocoapods (#496)

* Build as many dependencies as possible with SPM.
* Xcworkspace is no longer needed.
* Collecting coverage information does unfortunately cause linking errors in Base32. So it is disabled for now.

.github/workflows/testing.yml

@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
   testing:
-    runs-on: macos-latest
+    runs-on: macos-11
     steps:
     - uses: actions/checkout@v2
     - name: Installing packages
@@ -20,12 +20,6 @@ jobs:
         key: ${{ runner.os }}-carthage-${{ secrets.CACHE_VERSION }}-${{ hashFiles('**/Cartfile.resolved') }}
         restore-keys: |
           ${{ runner.os }}-carthage-${{ secrets.CACHE_VERSION }}-
-    - uses: actions/cache@v2
-      with:
-        path: Pods
-        key: ${{ runner.os }}-pods-${{ secrets.CACHE_VERSION }}-${{ hashFiles('**/Podfile.lock') }}
-        restore-keys: |
-          ${{ runner.os }}-pods-${{ secrets.CACHE_VERSION }}-
     - uses: actions/cache@v2
       id: gopenpgp-cache
       with:
@@ -37,8 +31,6 @@ jobs:
       run: |
         bundle config path vendor/bundle
         bundle install --jobs 4 --retry 3
-    - name: Cocoapods
-      run: bundle exec pod install
     - name: Carthage
       if: steps.carthage-cache.outputs.cache-hit != 'true'
       run: |