local paths in directories are not included correctly.

[MrGreenTea]

When I have this structure:

❯ tree doc
doc
├── conf.py
├── examples
│      └──  example.cast
└── index.rst

And try to include example.cast in index.rst like this: .. asciinema:: examples/example.cast the built html will not be able to access the cast. It seems this is because example.cast is put top level into the generated hash directory in build/_casts/ but the reference in the index.html points to _casts/<hash>/examples/example.cast instead of at _casts/<hash>/example.cast.