Fbs

Pertaining to the new commands

* `sign_installer`
* `repo`
* `buildvm`

The command generates a repository for your app in `target/repo`. For example:

(venv) michael:~/Temp$ fbs runvm ubuntu
(venv) ubuntu:MyApp$ fbs clean
(venv) ubuntu:MyApp$ fbs freeze
(venv) ubuntu:MyApp$ fbs installer
(venv) ubuntu:MyApp$ fbs repo
Done. You can test the repository with the following commands:
echo "deb [arch=amd64] file:///root/MyApp/target/repo stable main" | sudo tee /etc/apt/sources.list.d/myapp.list
sudo apt-key add /root/MyApp/src/sign/linux/public-key.gpg
sudo apt-get update
sudo apt-get install myapp
To revert these changes:
sudo dpkg --purge myapp
sudo apt-key del 14094467C98844FA757D5BF1E954B8C89764F1AC
sudo rm /etc/apt/sources.list.d/myapp.list
sudo apt-get update

The next step is to upload the repository to a web server. Then, your users can simply execute the above commands `apt-key add` etc. to install your app. What's more, when you publish a new version of your app to the server, your users will automatically receive it.

This is in preparation for supporting code signing on Linux.

Suppose you want your app to run on Ubuntu. Your development machine runs Ubuntu 18. But you also want users on Ubuntu 16 to be able to execute your app.

The (shared) libraries on Linux systems are normally not backwards-compatible. This means that, most likely, when you build your app on Ubuntu 18, then it won't run on Ubuntu 16.

To solve this, fbs now lets you use [Docker](https://www.docker.com/) virtual machines for building your app. This lets you build your app inside a virtual machine (=Docker container) running Ubuntu 14. That way, everyone on Ubuntu 14+ can run your app.

There are now two new commands: `fbs buildvm <name>` and `fbs runvm <name>`. The first initializes the given Docker container; the latter runs it. Here's what this looks like:

Initialise the container:

(venv) michael:~/Temp$ fbs buildvm ubuntu
Done. You can now execute:
fbs runvm ubuntu

Run it:

(venv) michael:~/Temp$ fbs runvm ubuntu
You are now in a Docker container running Ubuntu. To build your app
for this platform, use the normal commands `fbs freeze` etc.

Note that you can't launch GUIs here. So eg. `fbs run` won't work.

Another caveat is that target/ is special here: It symlinks to your
usual target/ubuntu/. So when you are done and type `exit` to leave
this container, you can find the produced binaries there.

Freeze your app. Note how the `ubuntu:` prefix indicates that you are inside the VM:

(venv) ubuntu:MyApp$ fbs freeze

Exit the container:

(venv) ubuntu:MyApp$ exit

Now, back outside the VM, run the binary that was just produced. Note the `ubuntu/` subdirectory of the `target/` directory:

(venv) michael:~/Temp$ target/ubuntu/MyApp/MyApp

In addition to `ubuntu`, fbs currently supports `arch` and `fedora` for building for Arch and Fedora Linux, respectively.

'Resources' made it sound like it only applies to `src/main/resources`.
But it also applies to eg. `src/freeze/...`.