added Wextra to src compilation flags, ref #53
added dummy constructors for ESOptimizer and CMAStrategy as convenience for declaring object in external classes + used pointer for fplotstream as streams are not copyable

Conflicts:
	src/cmastrategy.cc
	src/cmastrategy.h
support for control of size of in-memory history used in equalfunvals stopping criteria: allows to run in constant-size memory when solving very large optimization problems