Kind attribute omitted

[shikolay]

Currently absence of kind attribute cause captionator to throw exception, but according to specs:
if there is no kind attribute, implementation need consider this as 'subtitles' kind.

From specs:
The attribute(kind) may be omitted. The missing value default is the subtitles state.

[cgiffard]

Yeah, this probably changed since I implemented the spec (ages and ages ago.)

I'll make this small change for you, but I am looking to entirely rewrite the project.