[yt-dev] Issue #634: Set up derived quantities for individual particle types (yt_analysis/yt)

[Matthew Turk]

New issue 634: Set up derived quantities for individual particle types
https://bitbucket.org/yt_analysis/yt/issue/634/set-up-derived-quantities-for-individual

Matthew Turk:

Much like how we have the `particle_fields.py` file for creating specific types of particle fields, we should have this for derived quantities as well.

Responsible: MatthewTurk