Help: De-duplicate and spell out supported hash algorithms

Spell out the supported algorithms in a definition list in the
`string(<HASH>)` command documentation.  Revise the `file(<HASH>)`
command and CPack module documentation to reference it instead of
duplicating the list.

Help/command/file.rst

@@ -83,10 +83,12 @@ from the input file.
 
 ::
 
-  file(<MD5|SHA1|SHA224|SHA256|SHA384|SHA512> <filename> <variable>)
+  file(<HASH> <filename> <variable>)
 
 Compute a cryptographic hash of the content of ``<filename>`` and
-store it in a ``<variable>``.
+store it in a ``<variable>``.  The supported ``<HASH>`` algorithm names
+are those listed by the :ref:`string(\<HASH\>) <Supported Hash Algorithms>`
+command.
 
 ------------------------------------------------------------------------------
 
@@ -234,8 +236,8 @@ Additional options to ``DOWNLOAD`` are:
 ``EXPECTED_HASH ALGO=<value>``
 
   Verify that the downloaded content hash matches the expected value, where
-  ``ALGO`` is one of ``MD5``, ``SHA1``, ``SHA224``, ``SHA256``, ``SHA384``, or
-  ``SHA512``.  If it does not match, the operation fails with an error.
+  ``ALGO`` is one of the algorithms supported by ``file(<HASH>)``.
+  If it does not match, the operation fails with an error.
 
 ``EXPECTED_MD5 <value>``
   Historical short-hand for ``EXPECTED_HASH MD5=<value>``.

Help/command/string.rst

@@ -206,15 +206,30 @@ Comparison
 
 Compare the strings and store true or false in the output variable.
 
+.. _`Supported Hash Algorithms`:
+
 Hashing
 ^^^^^^^
 
 ::
 
-  string(<MD5|SHA1|SHA224|SHA256|SHA384|SHA512>
-         <output variable> <input>)
+  string(<HASH> <output variable> <input>)
 
 Compute a cryptographic hash of the input string.
+The supported ``<HASH>`` algorithm names are:
+
+``MD5``
+  Message-Digest Algorithm 5, RFC 1321.
+``SHA1``
+  US Secure Hash Algorithm 1, RFC 3174.
+``SHA224``
+  US Secure Hash Algorithms, RFC 4634.
+``SHA256``
+  US Secure Hash Algorithms, RFC 4634.
+``SHA384``
+  US Secure Hash Algorithms, RFC 4634.
+``SHA512``
+  US Secure Hash Algorithms, RFC 4634.
 
 Generation
 ^^^^^^^^^^

Modules/CPack.cmake

@@ -126,7 +126,9 @@
 #
 #     ${CPACK_PACKAGE_FILE_NAME}.${CPACK_PACKAGE_CHECKSUM}
 #
-#  Current supported alogorithms: MD5|SHA1|SHA224|SHA256|SHA384|SHA512.
+#  Supported algorithms are those listed by the
+#  :ref:`string(\<HASH\>) <Supported Hash Algorithms>`
+#  command.
 #
 # .. variable:: CPACK_PROJECT_CONFIG_FILE
 #