fix has_xx_type meta funciton to out of unnamed namespace.
rename macro name

NEK_DEFINE_HAS_XXX_TYPE -> NEK_HAS_XXX_TYPE_DEF
rename macro name

NEK_IS_XXX -> NEK_IS_XXX_DEF
change coding style

 const T -> T const
update READMe.md

 * support Visual C++ 12.0 CTP.
 * update a Purpose.