function insert(subject, toInsert, position) {
    var subjectString = coerceToString(subject);
    var toInsertString = coerceToString(toInsert);
    var positionNumber = coerceToNumber(position);

    if (positionNumber < 0 || positionNumber > subjectString.length || toInsertString === '') {
      return subjectString;
    }

    return subjectString.slice(0, positionNumber) + toInsertString + subjectString.slice(positionNumber);
  }
Inserts into `subject` a string `toInsert` at specified `position`.

@function insert
@static
@since 1.0.0
@memberOf Manipulate
@param {string} [subject=''] The string where to insert.
@param {string} [toInsert=''] The string to be inserted.
@param {number} [position=0] The position to insert.
@return {string} Returns the string after insertion.
@example
v.insert('ct', 'a', 1);
// => 'cat'

v.insert('sunny', ' day', 5);
// => 'sunny day'