[FEATURE] Release based on upstream Stan v2.36

[yizhang-yiz]

Description

Plan for next release. In particular, to support tinystan, see flatironinstitute/stan-playground#289 (comment).

Items

• New documentation.
• Merge Stan v2.36
• [FEATURE] Analytical gradients similar to how NONMEM does mu-referencing #76

Current Version:

v0.91.1

[yizhang-yiz]

@cbdavis33 @billgillespie @charlesm93 let me know if you have additional items go into next release.