DOC: Fix some references

[takanori-pskq]

Related to #13114.

[eric-wieser]

Perhaps out of scope, but this is quite out of date - the full list is:

numpy/numpy/core/include/numpy/ufuncobject.h

Lines 281 to 311 in c004383

	/*
	* UFunc has unit of 0, and the order of operations can be reordered
	* This case allows reduction with multiple axes at once.
	*/
	#define PyUFunc_Zero 0
	/*
	* UFunc has unit of 1, and the order of operations can be reordered
	* This case allows reduction with multiple axes at once.
	*/
	#define PyUFunc_One 1
	/*
	* UFunc has unit of -1, and the order of operations can be reordered
	* This case allows reduction with multiple axes at once. Intended for
	* bitwise_and reduction.
	*/
	#define PyUFunc_MinusOne 2
	/*
	* UFunc has no unit, and the order of operations cannot be reordered.
	* This case does not allow reduction with multiple axes at once.
	*/
	#define PyUFunc_None -1
	/*
	* UFunc has no unit, and the order of operations can be reordered
	* This case allows reduction with multiple axes at once.
	*/
	#define PyUFunc_ReorderableNone -2
	/*
	* UFunc unit is an identity_value, and the order of operations can be reordered
	* This case allows reduction with multiple axes at once.
	*/
	#define PyUFunc_IdentityValue -3

[takanori-pskq]

Fixed.

[eric-wieser]

Suggested change

	To work the examples, you'll need ``matplotlib`` installed
	To work the examples, you'll need :mod:`matplotlib` installed

assuming we have intersphinx set up.

[mattip]

Thanks @takanori-pskq. Only 333 more warning to go until we can turn on -n