just removed redefined 'unlikely' macro
Remove unused add method accepting vectors

This function is no longer used by PyStan and it is, moreover, designed
incorrectly. In RStan and PyStan chains are effectively stored in "row order" as
each parameter has its own vector<double> of size `num_iter`. This function
assumes this arrangement is transposed, that one has has `num_iter` vectors.
moved likely and unlikely macros to their own header files
updating definitions of macros likely and unlikely
Merge pull request #1020 from ariddell/feature/remove-chains-add-method

Remove unused add method accepting vectors
replaced int with size_t to stop g++ griping about signed/unsigned comparisons in integrate_ode
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/issue-771-ode-solver
Merge pull request #1018 from stan-dev/feature/issue-1002-unlikely-macro-redefined

Remove warning for 'unlikely' macro redefinition
fixed merge conflict by removing chunk_alloc again
updated manual with new notation for data in ode calls
created new stan-reference/img directory and moved images used in doc to there
updated stan-reference doc with links to new img subdirectory for images