Merge pull request #388 from stan-dev/feature/issue-323-size-decl-types

Fixes #323.
Merge branch 'hotfix/v2.0.2' of https://github.com/stan-dev/stan into hotfix/v2.0.2
analytic gradients for sd, variance, new vari impl for stored gradients, plus tests, doc
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
getting test-headers to pass
Merge branch 'develop' into bugfix/issue-379-sd-grad-at-0

Conflicts:
	src/stan/agrad/matrix.hpp
removed compiler warnings
Merge pull request #414 from stan-dev/bugfix/issue-379-sd-grad-at-0

fixes #379.