rstan_rebuild_trajectory: Recreate an HMC trajectory
In jtimonen/stanbreaker: Fast way to try out different things in Stan

Recreate an HMC trajectory given a parameter and momentum draw, a maximum number of leapfrog steps to take, a stepsize, and an inverse metric.

1	rstan_rebuild_trajectory(fit, udraws, mdraws, leapfrogs, stepsize, inv_metric)

`fit`	An rstan stanfit object
`udraws`	A vector of unconstrained parameters to start the trajectory from
`mdraws`	A vector of momentums to start the trajectory from
`leapfrogs`	Number of leapfrog steps to integrate in each direction
`stepsize`	Stepsize for leapfrog integrator
`inv_metric`	Positive definite inverse metric