* BOOST_MATH_EXPORT on the 38 distribution class templates (fwd.hpp and
definition sites), every non-member accessor overload, the convenience
typedefs, the complement machinery and find_location/find_scale
* distributions/fwd.hpp now includes tools/config.hpp so the export
macro is always defined
* Adds distributions.hpp to the module interface unit
* Module test harness gains git_issue_1294, git_issue_800,
git_issue_1120 and scipy_issue_17146
Matt Borland