Shuffling around public vs. private headers

Shuffling around public vs. private headers
- Adding a script contrib/test_install_headers.h that tests whether one can include all cvc4_public headers. CVC4 can pass this test after this commit.
- Making lib/{clock_gettime.h,ffs.h,strtok_r.h} cvc4_private.
- Making prop/sat_solver_factory.h cvc4_private.
- Moving the expr iostream manipulators into their own files: expr_iomanip.{h,cpp}.
- Setting the generated *_options.h files back to being cvc4_private.
-- Removing the usage of options/expr_options.h from expr.h.
-- Removing the include of base_options.h from options.h.
- Cleaning up CPP macros in cvc4_public headers.
-- Changing the ROLL macro in floatingpoint.h into an inline function.
-- Removing the now unused flag -D__BUILDING_STATISTICS_FOR_EXPORT.