bpo-40204: Fix reference to terms in the doc (GH-21865)

Sphinx 3 requires to refer to terms with the exact case.

For example, fix the Sphinx 3 warning:

Doc/library/pkgutil.rst:71: WARNING: term Loader not found in case
sensitive match.made a reference to loader instead.
diff --git a/Doc/library/collections.abc.rst b/Doc/library/collections.abc.rst
index 2a3fb14..dc7ae30 100644
--- a/Doc/library/collections.abc.rst
+++ b/Doc/library/collections.abc.rst
@@ -185,7 +185,7 @@
    expressions.  Custom implementations must provide the :meth:`__await__`
    method.
 
-   :term:`Coroutine` objects and instances of the
+   :term:`Coroutine <coroutine>` objects and instances of the
    :class:`~collections.abc.Coroutine` ABC are all instances of this ABC.
 
    .. note::
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst
index b21d559..675a9ff 100644
--- a/Doc/library/concurrent.futures.rst
+++ b/Doc/library/concurrent.futures.rst
@@ -221,7 +221,8 @@
 The :class:`ProcessPoolExecutor` class is an :class:`Executor` subclass that
 uses a pool of processes to execute calls asynchronously.
 :class:`ProcessPoolExecutor` uses the :mod:`multiprocessing` module, which
-allows it to side-step the :term:`Global Interpreter Lock` but also means that
+allows it to side-step the :term:`Global Interpreter Lock
+<global interpreter lock>` but also means that
 only picklable objects can be executed and returned.
 
 The ``__main__`` module must be importable by worker subprocesses. This means
diff --git a/Doc/library/importlib.rst b/Doc/library/importlib.rst
index f7286d2..5fb0a4a 100644
--- a/Doc/library/importlib.rst
+++ b/Doc/library/importlib.rst
@@ -1073,7 +1073,7 @@
 
 .. class:: WindowsRegistryFinder
 
-   :term:`Finder` for modules declared in the Windows registry.  This class
+   :term:`Finder <finder>` for modules declared in the Windows registry.  This class
    implements the :class:`importlib.abc.MetaPathFinder` ABC.
 
    Only class methods are defined by this class to alleviate the need for
@@ -1088,7 +1088,7 @@
 
 .. class:: PathFinder
 
-   A :term:`Finder` for :data:`sys.path` and package ``__path__`` attributes.
+   A :term:`Finder <finder>` for :data:`sys.path` and package ``__path__`` attributes.
    This class implements the :class:`importlib.abc.MetaPathFinder` ABC.
 
    Only class methods are defined by this class to alleviate the need for
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 69d6523..28510ac 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -14,7 +14,8 @@
 :mod:`multiprocessing` is a package that supports spawning processes using an
 API similar to the :mod:`threading` module.  The :mod:`multiprocessing` package
 offers both local and remote concurrency, effectively side-stepping the
-:term:`Global Interpreter Lock` by using subprocesses instead of threads.  Due
+:term:`Global Interpreter Lock <global interpreter lock>` by using
+subprocesses instead of threads.  Due
 to this, the :mod:`multiprocessing` module allows the programmer to fully
 leverage multiple processors on a given machine.  It runs on both Unix and
 Windows.
diff --git a/Doc/library/pkgutil.rst b/Doc/library/pkgutil.rst
index 2066cbb..3b17b9a 100644
--- a/Doc/library/pkgutil.rst
+++ b/Doc/library/pkgutil.rst
@@ -68,7 +68,7 @@
 
 .. class:: ImpLoader(fullname, file, filename, etc)
 
-   :term:`Loader` that wraps Python's "classic" import algorithm.
+   :term:`Loader <loader>` that wraps Python's "classic" import algorithm.
 
    .. deprecated:: 3.3
       This emulation is no longer needed, as the standard import mechanism
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 458e39b..7fcf93d 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -394,7 +394,8 @@
 
 .. impl-detail::
 
-   In CPython, due to the :term:`Global Interpreter Lock`, only one thread
+   In CPython, due to the :term:`Global Interpreter Lock
+   <global interpreter lock>`, only one thread
    can execute Python code at once (even though certain performance-oriented
    libraries might overcome this limitation).
    If you want your application to make better use of the computational