spow

import des.math.linear.vector;
assert( spow( vec3( 1, 2, 3 ), 3 ) == vec3( 1, 8, 27 ) );
assert( spow( 10, 0 ) == 1 );
assert( spow( 10, 1 ) == 10 );
assert( spow( 10, 2 ) == 100 );
assert( spow( 10, 3 ) == 1000 );
assert( spow( 10, 4 ) == 10000 );