Allow stan::math::minus on std::vectors

[WardBrian]

Summary

This applies the vectorization framework to stan::math::minus to allow it to be applied to std::vectors and other containers.

Tests

Existing tests are updated to test vectorization, and a test is added to ensure the return type of std::vector<int> is std::vector<int>

Side Effects

None

Release notes

stan::math::minus can now accept std::vectors.

Checklist

• Math issue : Feature request: make unary negation vectorized stanc3#529

• Copyright holder: Simons Foundation

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[andrjohns]

LGTM! Thanks @WardBrian