Fix referencing video files from any path

[QuLogic]

This makes it no longer necessary to place video files in _static, but instead in any location.

I spent a while going through Shinx's implementation for images, and this copies what it does:

1. File paths are normalized with Environment.relfn2path, and also a dependency is added for the document in the Environment. This allows paths relative to any document.
2. A post transform adds the files from the Environment to a tracker on the Builder. This causes the HTML5 builder to copy the file to the _images directory (and a unique name is guaranteed by the tracker on the Environment).
3. The URI is re-written to be relative to the builder image path (only when using HTML output.)

Fixes #33
Because Sphinx then tries to copy the file, it raises a warning if not found, so I think this also fixes (partially) #14. However, if you expected the file to be in the _static directory, it might not warn. I did not check that.

[severin-lemaignan]

I've tested the patch and it works brilliantly for me (also with 2 video sources). Thanks!

[12rambau]

I really like this update, aligning on how image directive is working is a very good thing.
Could you update the documentation to reflect this change there as well ?

I also see that mypy is unhappy with typing checks can you have a look to the latest build ?

[12rambau]

I'll merge it with master once the tests are happy and create a release candidate to let people play with it. As it's changing how images are referenced it's important to give people a heads up.

@QuLogic can you have a look to the mypy issues ?

[QuLogic]

The mypy issue seems unrelated; I can reproduce it on master. I see previous workflows passed, so maybe something in Sphinx changed recently?

[QuLogic]

See #37.

[Calinou]

I see the version was bumped to 0.2.1rc0 in 098b467. Could this be published on PyPI (perhaps as 0.2.1) so that it can be referenced in Sphinx repositories? This would unblock me for integrating videos on godot-docs. Thanks in advance 🙂

[QuLogic]

It is on PyPI: https://pypi.org/project/sphinxcontrib-video/0.2.1rc0/ (you'd need to pass --pre to pip install to see it, or explicitly ask for that version.)