cmd: Add new cli command

This command can be used to print the current parser with 'cli get'.
It can also be used to set the current parser with 'cli set'.
For the moment, only one value is valid for set: old.

Signed-off-by: Francis Laniel <francis.laniel@amarulasolutions.com>

doc/usage/cmd/cli.rst

@@ -0,0 +1,59 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+cli command
+===========
+
+Synopis
+-------
+
+::
+
+    cli get
+    cli set cli_flavor
+
+Description
+-----------
+
+The cli command permits getting and changing the current parser at runtime.
+
+cli get
+~~~~~~~
+
+It shows the current value of the parser used by the CLI.
+
+cli set
+~~~~~~~
+
+It permits setting the value of the parser used by the CLI.
+
+Possible values are old and 2021.
+Note that, to use a specific parser its code should have been compiled, that
+is to say you need to enable the corresponding CONFIG_HUSH*.
+Otherwise, an error message is printed.
+
+Examples
+--------
+
+Get the current parser::
+
+    => cli get
+    old
+
+Change the current parser::
+
+    => cli set old
+
+Trying to set the current parser to an unknown value::
+
+    => cli set foo
+    Bad value for parser name: foo
+    cli - cli
+
+    Usage:
+    cli get - print current cli
+    set - set the current cli, possible value is: old
+
+Return value
+------------
+
+The return value $? indicates whether the command succeeded.

doc/usage/index.rst

@@ -43,6 +43,7 @@ Shell commands
    cmd/cat
    cmd/cbsysinfo
    cmd/cedit
+   cmd/cli
    cmd/cls
    cmd/cmp
    cmd/coninfo