src: Move <a-m> to <a-_>

doc/pages/keys.asciidoc

@@ -258,7 +258,7 @@ Yanking (copying) and pasting use the *"* register by default (See <<registers#,
 *<a-J>*::
     join selected lines and select spaces inserted in place of line breaks
 
-*<a-m>*::
+*<a-_>*::
     merge contiguous selections together (works across lines as well)
 
 *>*::

src/normal.cc

@@ -2185,7 +2185,7 @@ static const HashMap<Key, NormalCmd, MemoryDomain::Undefined, KeymapBackend> key
     { {';'}, {"reduce selections to their cursor", clear_selections} },
     { {alt(';')}, {"swap selections cursor and anchor", flip_selections} },
     { {alt(':')}, {"ensure selection cursor is after anchor", ensure_forward} },
-    { {alt('m')}, {"merge consecutive selections", merge_consecutive} },
+    { {alt('_')}, {"merge consecutive selections", merge_consecutive} },
 
     { {'w'}, {"select to next word start", repeated<&select<SelectMode::Replace, select_to_next_word<Word>>>} },
     { {'e'}, {"select to next word end", repeated<select<SelectMode::Replace, select_to_next_word_end<Word>>>} },