Extract model inputs directly from the compiler

[MansMeg]

This is an issue started from the following PR #192

Ping @mandel.

[mandel]

Thank you for opening this issue.

I have updated the fork of the Stan compiler to add an option --info which outputs on the standard output a JSON object containing information about the model. It currently generates an object a field inputs containing a dictionary where each entry corresponds to a variable in the data block. To each variable is associated an object with two fields:

• type: the base type of the variable ("int" or "real").
• dimensions: the number of dimensions (0 for a scalar, 1 for a vector or row vector, etc.).

The code is available in the info branch of the fork: https://github.com/mandel/stanc3/tree/info

[MansMeg]

Thanks! I will try to add this to the documentation somehow. Thanks!