/*
 *  call-seq:
 *     dvector.tanh!   ->  dvector
 *  
 *  Replace each entry x of _dvector_ with tanh(x).
 *     
 *     a = Dvector[ 1.1, -2.2, 5.3 ]
 *     a.tanh!   -> Dvector[ tanh(1.1), tanh(-2.2), tanh(5.3) ]
 *     a         -> Dvector[ tanh(1.1), tanh(-2.2), tanh(5.3) ]
 */ 
VALUE dvector_tanh_bang(VALUE ary) {