Track language and library versions separately (#289)
Track language and library versions separately (#289)

* Add `gsl_STDLIB_CPPxx_OR_GREATER` macros to track standard library availability
* Add library feature detection macros `gsl_HAVE( HASH )`, `gsl_HAVE( MOVE_FORWARD )`
martinmoene/gsl-lite,martinmoene/gsl-lite,martinmoene/gsl-lite