/// Selection Sort
///
/// Input: mutable reference of vector x of n elements
/// Post-condition: sorted vector of n elements
///
/// ================================================================================================
///
/// ```ignore
/// loop n elements in x setting index to i
/// set minimum_index = i
/// loop i + 1 elements in x setting index to j
/// if x[j] < x[minimum_index] then
/// minimum_index = j
/// swap minimum index in x with i in x
/// ```