removing more warnings
fixed a bad cast in trying to remove warnings
adding casts to segmeent to reduce warnings
Merge branch 'feature/issue-682-remove-warnings-v2.3.0' of https://github.com/stan-dev/stan into feature/issue-682-remove-warnings-v2.3.0
removed more warnings
Merge pull request #689 from stan-dev/feature/issue-682-remove-warnings-v2.3.0

Fixes #682. Feature/issue 682 remove warnings v2.3.0
updating version numbers
updating RELEASE-NOTES.txt
adding doc/stan-reference-2.3.0.pdf as an artifact
Merge pull request #691 from stan-dev/feature/issue-690-tag-v2.3.0

Fixes #690. Feature/issue 690 tag v2.3.0
removed doc/stan-reference-2.3.0.pdf
Merge pull request #693 from stan-dev/feature/issue-692-remove-artifacts

Fixes #692. removed doc/stan-reference-2.3.0.pdf
Merge branch 'develop' into feature/issue-676-generalize-operandsandpartials