Add GitHub Actions build and auto-release workflow

[ronaldtse]

This fixes #23.

Some users use Lato in their continuous integration builds (e.g. publishing PDFs, such as in Metanorma).

As a user of Lato we have run into a few operational issues that could be solved:

1. The latest Lato fonts (3.100dev) are not available from the official website.
2. The official website font link becomes unavailable occasionally. (e.g. Lato font always unavailable from official URL fontist/formulas#112)

This PR provides a GitHub Actions workflow that:

• automatically publishes releases at the repository given a Git tag (e.g. v3.100.dev2)
• automatically builds fonts on changes in the master branch and PRs (according to instructions in the README)

[sergeevabc]

Dear @ronaldtse, it seems the latest build of Lato (version 3.1) is still not available on the official website. Nor has your appeal to change the situation been given the attention it deserves. But we should proceed somehow. Perhaps you could share .zip archive?

[ronaldtse]

@sergeevabc the latest release files (v3.100.dev.2) are available here:

• https://github.com/fontist/lato-source/releases/tag/v3.100.dev2

Hope this helps!

[sergeevabc]

Hooray! Thank you for a quick reply, sir. It works as intended.

[ronaldtse]

You're welcome @sergeevabc ! 😉

[applecuckoo]

@ronaldtse unless I'm mistaken I can't see the variable fonts in that release?