Add inverse_spd function which computes the inverse using the LDLT transform.
Add unit test for inverse_spd.
Documentation for inverse_spd
Expose inverse_spd to the parser.
In inverse_spd 0.5*(a + a') when computing LDLT to ensure that gradients are spread out and update tests.
Merge branch 'gp_improvements' of https://github.com/mbrubake/stan into gp_improvements
Add propto default for matrix_normal_prec_log and tweak error handling.
Add unit test for matrix_normal_prec distribution.