Allow the user to record and run a single macro.  The default binding
for starting and stopping the recording is M-: (Alt + colon) and for
running the macro M-; (Alt + semicolon).

This fulfills https://savannah.gnu.org/bugs/?50314

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Requested-by: Peter Passchier <peter@passchier.net>
Signed-off-by: Marco Diego Aurélio Mesquita <marcodiegomesquita@gmail.com>
Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>