Update cvodes to 3.1.0

Add passing by reference for matrix_exp function.

Fixes #736. add boost mpi, boost build and dependencies

This reverts commit f0993c18, reversing
changes made to ad01b2cc.

Bugfix/issue 525 d gamma cdf da

bcp mpi build stan-math/lib/boost_BOOST_VERSION
cd stan-math/lib/boost_BOOST_VERSION
find . -name "doc" -type d -exec rm -rf {} ;
find . -name "example" -type d -exec rm -rf {} ;
find libs -name "test" -type d -exec rm -rf {} ;

Split out travis tests further

Adding top-level license file

boost 1.66, fixes #765

Feature/issue 706 mdivide right

fixes #698, renamed multi-caps tparam in algebra system

Add IDAS package from SUNDIALS into stan math libs. Update makefile