Feature/0370 remove math.h dependency for C99/C++11 functions

[bob-carpenter]

Submisison Checklist

• Run unit tests: ./runTests.py test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary:

Remove all math.h and top-level namespace dependencies and remove all ifdefs for MSVC with namespace-level using of top-level includes.

Intended Effect:

Unify code, remove math.h top-level namespaces, and pave the way for vectorizing the remaining functions.

How to Verify:

Unit tests still pass. More unit tests for new primitive functions.

Side Effects:

Requires updates to stan-dev/stan to qualify the new functions rather than namespace using statements.

Documentation:

Added doc to functions that needed it.

Reviewer Suggestions:

Anyone.

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company):

Columbia University

By submitting this pull request, the copyright holder is agreeing to 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/)

[syclik]

Awesome!