Feature Proposal Feedback: adding `jacobian` keyword and a new `constraints` block to the Stan language

I posted a design doc that adds a new keyword jacobian to the Stan language along with a new block constraints that will allow users to define their own constraint types. If you have any feedback or comments on the proposal please comment in the design doc linked below


The place to post comments for this is on the design doc pull request. Feel free to drop in individual comments there which we’ll take into account when doing a final review.