Valentin Boettcher authored Oct 04, 2019 and Frank Siegert committed Oct 04, 2019

1. I've forced parallel build for the manual to fix race conditions found by @fsiegert.
   `MAKEFLAGS=-j1` is *not* overwritten by the `-j` flag on the command ...
2. I had forgotten a left over command line argument for the multi version manual build in the ci and removed it.
3. I've added a new build step to test the build process for the manual. The multi version build and the deployment to pages is only performed on tags and on commits to master.