Merge branch 'develop' of https://github.com/stan-dev/stan into develop
added cholesky_factor to ast, grammars, code generator
added checks for cholesky and lower triangular
added cholesky factor transform to prob/transform.hpp with tests and some extra error handling cleanup
added reader and writer for square Cholesky, which is now feature complete and unit tested
finished merge
support for rectangular cholesky factors for covariance
added square Cholesky factor declaration form with only one dimension
updated manual with cholesky_factor_cov type syntax and transform definitions
slight doc cleanup for transform.hpp
Merge pull request #168 from stan-dev/feature/cholesky_factor_type

Feature/cholesky factor type