Add missing Attachment codec types

[Euklios]

Is your feature request related to a problem? Please describe.
FFmpeg codecs can handle video, audio, subtilte, and data streams, as implemented by this wrapper.
However, additionally attachment codecs are supported.

Describe the solution you'd like
Add ATTACHMENT to Codec enum.

Describe alternatives you've considered
The only solution I'm aware of is to ignore it.
Default builds of ffmpeg don't include any attachment codecs.
However, as it is supported, we should implement it as well.
Additionally, this makes the Codec.Type enum equal to the CodecType enum, which means we could merge them.
This also makes sense in a logical way, a stream has been encoded with CodecType, therefore encoding using a Codec with the same type would be reasonable