Merge pull request #557 from stan-dev/v1.16.0

Prepare for v1.16.0

Update NEWS.md

Bump version to 1.13.0 for CRAN submission

Merge pull request #341 from stan-dev/prep-v1.12.0

Prepare v1.12.0 for release

Update DESCRIPTION

Update .gitignore

fix error in example

bump date for CRAN submission

fix url