Cleaning up a few comments and doxygen documentation.

Also want to correct previous commit comment in that in the case of the
polysolve / sturm chain method the polish is correcting an all >0 drift
which causes an issue given the large scales and bezier normalization.
The current polysolve code clamps roots to >=0.0.

Author: wfpokorny

source/core/math/polynomialsolver.cpp

@@ -153,11 +153,7 @@ const PRECISE_FLOAT RELERROR = (PRECISE_FLOAT)1.0e-12;
 /// @var SMALL_ENOUGH
 /// const @ref DBL value used to filter determinant value in older
 /// solve_quadratic() in an unusual way causing artifacts. Used too in
-/// solve_quartic() to filter values ahead of the trailing quadratics.
-///
-/// @todo
-///     Suspect value is larger than it should really be and very likely should
-///     not be used at all in solve_quartic() as it is.
+/// solve_quartic() and polysolve() for root polishing threshold.
 ///
 const DBL SMALL_ENOUGH = 1.0e-10;