[WIP] Tiered annotations

[hadware]

Old idea, finally took some time to implement it.

This is more or less an implementation of the Praat/Elan tiered structure. Here are a couple of key points for this

• There are two data structures TieredAnnotation and Tier. A TieredAnnotation is made out of Tiers
• The structure is basically and schematically a dict of dict : TieredAnnotation[str, Tier[Segment,Label]]
• A Tier is a thin wrapper over a timeline, used to keep store segments and take care of the cropping/support/etc-related operations
• The TieredAnnotation shouldn't have that many available methods other than:
  • accessing tiers and tiers information
  • cropping/extruding/etc (all just done by the underlying Tiers)
  • Iterating over segment
• Support for textigrid files parsing is optional, and added by running pip install pyannote.core[textgrid]. This installs textgrid-parser, my sly-based parser.

I'll follow up with a couple of questions to tune my implem to your preferences

[hadware]

Alright, questions now:

• Since Tier is such a thin wrapper above Timeline, I'm wondering if I shouldn't just inherit from it. This would still require some methods to be overridden to make sure the returned type is right, but you get the point
• I've added the allow_overlap option to tiers to (optionally) more closely mimic TextGrid/Eaf's behavior. What do you think about that?
• I kind of modeled TieredAnnotation on Annotation, and thus, (for now) left the self._timeline attribute that is a "lazy" cache of the TieredAnnotation's timeline. I don't think this has any use anymore, but I wanted your opinion on this.

[hbredin]

Thanks @hadware. Will look into this at some point...