Support --input

[ullenboom]

It seems that --input is not recognized, but it would be useful to simulate:

asciinema rec --stdin demo.cast
asciinema play --stream=i demo.cast | asciinema rec new.cast

Trying:

...>PowerSession rec --stdin demo.cast
error: Found argument '--stdin' which wasn't expected, or isn't valid in this context

        If you tried to supply `--stdin` as a value rather than a flag, use `-- --stdin`

USAGE:
    PowerSession rec [OPTIONS] <file>

For more information try --help