Insert value at index.

		Args:
			index (int): Index to insert value at
			value: Value to insert
		Raises:
			ValueError: If value already in self
			IndexError: If start or end are out of range

def insert(self, index, value):
		"""Insert value at index.

		Args:
			index (int): Index to insert value at
			value: Value to insert
		Raises:
			ValueError: If value already in self
			IndexError: If start or end are out of range
		"""
		if value in self:
			raise ValueError
		index = self._fix_neg_index(index)
		self._dict[value] = index
		for elem in self._list[index:]:
			self._dict[elem] += 1
		self._list.insert(index, value)