docs: document the more everyday names of three bindable functions

List "browser", "pageup" and "pagedown" in the manuals; the first
because it matches "speller", and the latter two because they are
what these functions are commonly known by.  The names "tofiles",
"prevpage" and "nextpage" are now undocumented, but they are still
recognized by the code, as they match the tags for these functions.

doc/nano.texi

@@ -1203,10 +1203,10 @@ Moves the cursor to the beginning of the current or preceding block of text.
 @item nextblock
 Moves the cursor to the beginning of the next block of text.
 
-@item prevpage
+@item pageup
 Goes up one screenful.
 
-@item nextpage
+@item pagedown
 Goes down one screenful.
 
 @item firstline
@@ -1315,7 +1315,7 @@ When about to write a file, discard the current buffer without saving.
 (This function is bound by default only when option @option{--tempfile}
 is in effect.)
 
-@item tofiles
+@item browser
 Starts the file browser, allowing to select a file from a list.
 
 @item gotodir

doc/nanorc.5

@@ -562,10 +562,10 @@ Moves the cursor to the beginning of the current or preceding block of text.
 .B nextblock
 Moves the cursor to the beginning of the next block of text.
 .TP
-.B prevpage
+.B pageup
 Goes up one screenful.
 .TP
-.B nextpage
+.B pagedown
 Goes down one screenful.
 .TP
 .B firstline
@@ -674,7 +674,7 @@ When about to write a file, discard the current buffer without saving.
 (This function is bound by default only when option \fB\-\-tempfile\fR
 is in effect.)
 .TP
-.B tofiles
+.B browser
 Starts the file browser, allowing to select a file from a list.
 .TP
 .B gotodir