Fix documentation for constants

Sphinx cannot find the docstring corresponding to a constant unless you point
it to the exact file where it is, since it doesn't actually live on the object
itself. See sphinx-doc/sphinx#6495

Fixes #601

Author: asmeurer

spec/2021.12/API_specification/constants.rst

@@ -10,7 +10,7 @@ A conforming implementation of the array API standard must provide and support t
 Objects in API
 --------------
 
-.. currentmodule:: array_api
+.. currentmodule:: array_api.constants
 
 ..
   NOTE: please keep the functions in alphabetical order

spec/2022.12/API_specification/constants.rst

@@ -10,7 +10,7 @@ A conforming implementation of the array API standard must provide and support t
 Objects in API
 --------------
 
-.. currentmodule:: array_api
+.. currentmodule:: array_api.constants
 
 ..
   NOTE: please keep the functions in alphabetical order

spec/draft/API_specification/constants.rst

@@ -10,7 +10,7 @@ A conforming implementation of the array API standard must provide and support t
 Objects in API
 --------------
 
-.. currentmodule:: array_api
+.. currentmodule:: array_api.constants
 
 ..
   NOTE: please keep the functions in alphabetical order