adding src/stan/math/functions.hpp
rearranged stan/agrad/rev/ to match stan/math/
rearranged stan/agrad/fwd/ to match stan/math/
cleaned up top-level stan/agrad/*.hpp includes
Merge branch 'develop' into feature/issue-443-reorganize-agrad

cessary,
refactored init_adapt function to call a simpler init_adapt function that can be called through tests
adding a test that fails for init_adapt<>
fixed code to take in the appropraite starting value for init_adapt
Merge branch 'develop' into feature/issue-443-reorganize-agrad

Conflicts:
	src/stan/agrad/rev/matrix.hpp
Merge branch 'develop' into feature/issue-449-fix-initialization
merging develop. changing std::vector to Eigen::VectorXd
Merge pull request #450 from stan-dev/feature/issue-449-fix-initialization

Fixes #450.
fixed header guard
Merge pull request #457 from stan-dev/feature/issue-456-wrong-header-guard

Fixes #456.
Merge pull request #447 from stan-dev/feature/issue-443-reorganize-agrad

Fixes #443.
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/parser_error_reporting