Visual regression test

[zeptometer]

Merging this PR will close #4

Steps for running integration test:

1. Install SATySFi, Yarn, and GraphicsMagick
2. Run yarn install to install dependencies
3. Run yarn test to run tests

You can see the basic idea of the visual regression tests in this article.
Those tests will also run in GitHub Actions.

Future work:

• Add instruction on how to add/maintain visual regression tests
• Use appropriate class file instead of StdJa (cf. Create LaTeXiT-sh class file #14)

[zeptometer]

CI not working because of my wrong configuration🤔 I'll dig into it later.

[zeptometer]

Regression tests are passing in GitHub Actions👏

[zeptometer]

Now it's ready for review! I'd like feedback especially on

• Does __test__/README.md make enough sense to you?
• The existing test in t/ can be migrated to Jest snapshot tests in __test__. Do we wanna do that?

[nyuichi]

Does test/README.md make enough sense to you?

That is pretty clear to me :)

The existing test in t/ can be migrated to Jest snapshot tests in test. Do we wanna do that?

That helps a lot! Let's unify the language into JS for doing misc tasks in this repo.

[nyuichi]

LGTM