/// Insertion Sort
///
/// Input: mutable reference of vector x of n elements
/// Post-condition: sorted vector of n elements
///
/// ================================================================================================
///
/// ```ignore
/// loop over range from 2nd element to last in vector x
/// set insert_index to loop value
/// set current value using insert_index into vector x
/// while insert_index > 0 and previous value > current value
/// x[insert_index] = previous_value
/// subtract 1 from insert_index
///
/// x[insert_index] = current_value
/// ```