fixes #337. Builds Stan in 64-bit mode.
fixes #338. Windows build issue fixed where a model required .exe at the end
Fix the header guards for multi_normal_prec.hpp
Merge pull request #339 from stan-dev/feature/issue-337-win-build-64-bit

Windows build issues (#337 and #338)
Merge pull request #343 from mbrubake/feature/fix-multi_normal_prec-include

Fix the header guards for multi_normal_prec.hpp
Merge branch 'develop' into feature/fix-ldlt