File formats for video encodings and some PostScript files

[tiesont]

I've successfully added some FileFormat implementations / extensions that (seem to, in my use cases) correctly identity a small handful of video formats, like AVI or MP4.

Would a pull-request adding those formats to this project be useful, or would it make more sense to simply create an "add on" project (I'm leaning towards FileSignatures.VideoFormats as a name) which those who need video detection can use as needed?

I also implemented some formats that seem to correctly identify PSD or EPS files, although I'm not as confident on those. The same question from above would apply to these formats.

[neilharvey]

I'm happy to accept a pull request if it adds some useful formats, I'd always intended this to be written in such a way that the formats could be added to.