MATH-1008
Simplification of the code introduced in revision 1508481. The changes
only focus on the "fluent API" aspect (rather than also try to achieve
thread-safety through immutability).
Class "AbstractOptimizer" introduced to serve as the base class for all
optimizers (i.e. replace the current "BaseOptimizer").


git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1512530 13f79535-47bb-0310-9956-ffa450edef68