bindings: rename 'prevhistory' to 'older' and 'nexthistory' to 'newer'

Rename not only the bindable functions, but more importantly reword the
tags that are shown for ^P and ^N in the help lines: "Older" / "Newer",
because these are clearer and not awkward abbreviations.

doc/nano.texi

@@ -1312,11 +1312,11 @@ Toggles whether searching/replacing uses literal strings or regular expressions.
 @item backwards
 Toggles whether searching/replacing goes forward or backward.
 
-@item prevhistory
+@item older
-Retrieves the previous (older) entry at a prompt.
+Retrieves the previous (earlier) entry at a prompt.
 
-@item nexthistory
+@item newer
-Retrieves the next (newer) entry at a prompt.
+Retrieves the next (later) entry at a prompt.
 
 @item flipreplace
 Toggles between searching for something and replacing something.

doc/nanorc.5

@@ -673,11 +673,11 @@ Toggles whether searching/replacing uses literal strings or regular expressions.
 .B backwards
 Toggles whether searching/replacing goes forward or backward.
 .TP
-.B prevhistory
+.B older
-Retrieves the previous (older) entry at a prompt.
+Retrieves the previous (earlier) entry at a prompt.
 .TP
-.B nexthistory
+.B newer
-Retrieves the next (newer) entry at a prompt.
+Retrieves the next (later) entry at a prompt.
 .TP
 .B flipreplace
 Toggles between searching for something and replacing something.

src/global.c

@@ -657,9 +657,9 @@ void shortcut_init(void)
 	const char *regexp_gist =
 		N_("Toggle the use of regular expressions");
 #ifdef ENABLE_HISTORIES
-	const char *prevhistory_gist =
+	const char *older_gist =
 		N_("Recall the previous search/replace string");
-	const char *nexthistory_gist =
+	const char *newer_gist =
 		N_("Recall the next search/replace string");
 #endif
 #ifndef NANO_TINY
@@ -990,9 +990,9 @@ void shortcut_init(void)
 #endif
 #ifdef ENABLE_HISTORIES
 	add_to_funcs(get_history_older_void, MWHEREIS|MREPLACE|MREPLACEWITH|MWHEREISFILE,
-		N_("PrevHstory"), WITHORSANS(prevhistory_gist), TOGETHER, VIEW);
+		N_("Older"), WITHORSANS(older_gist), TOGETHER, VIEW);
 	add_to_funcs(get_history_newer_void, MWHEREIS|MREPLACE|MREPLACEWITH|MWHEREISFILE,
-		N_("NextHstory"), WITHORSANS(nexthistory_gist), BLANKAFTER, VIEW);
+		N_("Newer"), WITHORSANS(newer_gist), BLANKAFTER, VIEW);
 #endif
 
 #ifndef ENABLE_JUSTIFY
@@ -1605,9 +1605,9 @@ sc *strtosc(const char *input)
 			 !strcasecmp(input, "gototext"))  /* Deprecated.  Remove end of 2018. */
 		s->func = flip_goto;
 #ifdef ENABLE_HISTORIES
-	else if (!strcasecmp(input, "prevhistory"))
+	else if (!strcasecmp(input, "older"))
 		s->func = get_history_older_void;
-	else if (!strcasecmp(input, "nexthistory"))
+	else if (!strcasecmp(input, "newer"))
 		s->func = get_history_newer_void;
 #endif
 #ifndef NANO_TINY