Merge branch 'develop' of https://github.com/stan-dev/stan into develop

Merging upstream develop.
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Added sort_indices_* functions
Added sort_indices_* functions to the manual
Added functions sort_indices_* to function_signatures.h
revised doc, section titles, and added examples for sort functions
refactor of sort_indices_* functions based on Bob Carpenter's https://github.com/stan-dev/stan/pull/564#issuecomment-35143532
Adjustments in rev and fwd diff for the refactoring of sort_indices_* functions
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Changed name of template parameter to avoid compiler bug on Mac OS X 10.7.5.
Merge branch 'feature/sort_index' of https://github.com/stan-dev/stan into feature/sort_index
templated container out rather than type of std::vector or Eigen::Matrix
Merge pull request #569 from stan-dev/bugfix/issue-568-epil

Fixes #568.
A possible way to use to solve sign-compare warnings
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/parser_error_reporting
Fix two typos: "ane" and "rwo".
Revert "A possible way to use to solve sign-compare warnings"

This reverts commit c4a46eb1ff58bcfe27c5fd799ea9092ede42ed16.
hopefully this fixes the sign errors
adding function sigatures tests for sort_indicies
fixed unsigned comparison warnings inside tests