Merge branch 'develop' of https://github.com/stan-dev/stan into feature/fix-grammar-assoc-expected-op
made precedence of >> and > explicit in grammar rules
added include of <string> in ast.hpp
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/fix-grammar-assoc-expected-op
Merge pull request #88 from stan-dev/feature/fix-grammar-assoc-expected-op

Feature/fix grammar assoc expected op