Support Tuple indices in Stan CSV Header Reader

[WardBrian]

Submission Checklist

• Run unit tests: ./runTests.py src/test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary

With Tuples, it will no longer be the case that names will always look like x.1.2.1. You can also have a tuple separator indicated by :.

So, for example, a Stan expression x.1[1] will have header x:1.1, y[2].1[3] will be y.2:1.3

Intended Effect

Allow names with : in them for tuples to be parsed properly in the CSV reader

How to Verify

New test added with a header generated by the current compiler branch for Tuples

Side Effects

I also removed some functions no longer needed after #3179

Documentation

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company):
Simons Foundation

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[SteveBronder]

One small comment but otherwise looks good!