TalReader usage with new json structure

[LoganJF]

https://gist.github.com/LoganJF/838e1b885bb350becfea41852584f951

Hey, I'm having a bit of trouble accessing all the relevant features in the new format of the talirach using TalReader and JsonIndexReader (rather than the matlab path).

Specifically:

1. All the previous free-surfer information is gone (Loc1-5 fields)
2. List comprehension (with if else control flow) is required rather than broadcasting to extract out values

Can we add back this functionality?

[ariel215]

Addressed in #136 and #137