tweaks: unabbreviate "argument" in the documentation

Also, show that the argument in the extendsyntax format is not optional,
as any command requires at least one argument.  Also mention 'tabgives'
among the commands that are allowed in an included file.

doc/nano.1

@@ -282,7 +282,7 @@ at the width of the screen minus \fInumber\fR columns, allowing the wrap
 point to vary along with the width of the screen if the screen is resized.
 The default value is \-8.
 .TP
-.B "\-s ""\fIprogram\fR [\fIarg\fR...]\fB""\fR, \fB\-\-speller=""\fIprogram\fR [\fIarg\fR...]\fB"""
+.B "\-s ""\fIprogram\fR [\fIargument \fR...]\fB""\fR, \fB\-\-speller=""\fIprogram\fR [\fIargument \fR...]\fB"""
 Use this command to perform spell checking and correcting, instead of
 using the built-in corrector that calls \fBhunspell\fR or GNU \fBspell\fR.
 .TP

doc/nano.texi

@@ -403,8 +403,8 @@ point to vary along with the width of the screen if the screen is resized.
 The default value is @t{-8}.
 
 @anchor{@option{--speller}}
-@item -s "@var{program} [@var{arg} @dots{}]"
+@item -s "@var{program} [@var{argument} @dots{}]"
-@itemx --speller="@var{program} [@var{arg} @dots{}]"
+@itemx --speller="@var{program} [@var{argument} @dots{}]"
 Use the given program to do spell checking and correcting.  By default,
 @command{nano} uses the command specified in the @env{SPELL} environment
 variable.  If @env{SPELL} is not set, and @option{--speller} is
@@ -935,7 +935,7 @@ When needed, use @code{unset jumpyscrolling} instead.
 @item set softwrap
 Enable soft line wrapping for easier viewing of very long lines.
 
-@item set speller "@var{program} [@var{arg} @dots{}]"
+@item set speller "@var{program} [@var{argument} @dots{}]"
 Use the given program to do spell checking and correcting.
 @xref{@option{--speller}} for details.
 
@@ -1058,13 +1058,13 @@ file, to determine whether this syntax should be used for it.
 (This functionality only works when @code{libmagic} is installed
 on the system and will be silently ignored otherwise.)
 
-@item formatter @var{program} [@var{arg} @dots{}]
+@item formatter @var{program} [@var{argument} @dots{}]
 Run the given @var{program} on the full contents of the current buffer.
 (The current buffer is written out to a temporary file, the program is
 run on it, and then the temporary file is read back in, replacing the
 contents of the buffer.)
 
-@item linter @var{program} [@var{arg} @dots{}]
+@item linter @var{program} [@var{argument} @dots{}]
 Use the given @var{program} to do a syntax check on the current buffer.
 
 @item comment "@var{string}"
@@ -1117,10 +1117,11 @@ Read in self-contained color syntaxes from "syntaxfile".  Note that
 "syntaxfile" may contain only the above commands, from @code{syntax}
 to @code{icolor}.
 
-@item extendsyntax @var{name} @var{command} [@var{arg} @dots{}]
+@item extendsyntax @var{name} @var{command} @var{argument} @dots{}
 Extend the syntax previously defined as "@var{name}" with another @var{command}.
 This allows you to add a new @code{color}, @code{icolor}, @code{header},
-@code{magic}, @code{comment}, @code{linter}, or @code{formatter} command to an already
+@code{magic}, @code{formatter}, @code{linter}, @code{comment},
+or @code{tabgives} command to an already
 defined syntax --- useful when you want to slightly improve a syntax defined
 in one of the system-installed files (which normally are not writable).
 

doc/nanorc.5

@@ -264,7 +264,7 @@ When needed, use \fBunset jumpyscrolling\fR instead.
 .B set softwrap
 Enable soft line wrapping for easier viewing of very long lines.
 .TP
-.B set speller """\fIprogram\fR [\fIarg\fR...]\fB"""
+.B set speller """\fIprogram\fR [\fIargument \fR...]\fB"""
 Use the given \fIprogram\fR to do spell checking and correcting, instead of
 using the built-in corrector that calls \fBhunspell\fR or GNU \fBspell\fR.
 .TP
@@ -385,13 +385,13 @@ file, to determine whether this syntax should be used for it.
 (This functionality only works when \fBlibmagic\fP is installed on the
 system and will be silently ignored otherwise.)
 .TP
-.BI formatter " program " \fR[ "arg " \fR...]
+.BI formatter " program " \fR[ "argument " \fR...]
 Run the given \fIprogram\fR on the full contents of the current buffer.
 (The current buffer is written out to a temporary file, the program is
 run on it, and then the temporary file is read back in, replacing the
 contents of the buffer.)
 .TP
-.BI linter " program " \fR[ "arg " \fR...]
+.BI linter " program " \fR[ "argument " \fR...]
 Use the given \fIprogram\fR to run a syntax check on the current buffer.
 .TP
 .BI "comment """ string """
@@ -444,10 +444,11 @@ Read in self-contained color syntaxes from \fIsyntaxfile\fP.  Note that
 \fIsyntaxfile\fP may contain only the above commands, from \fBsyntax\fP
 to \fBicolor\fP.
 .TP
-.BI extendsyntax " name command " \fR[ "arg " \fR...]
+.BI extendsyntax " name command argument " \fR...
 Extend the syntax previously defined as \fIname\fR with another
 \fIcommand\fR.  This allows adding a new \fBcolor\fP, \fBicolor\fP,
-\fBheader\fP, \fBmagic\fP, \fBcomment\fP, \fBlinter\fP, or \fBformatter\fR
+\fBheader\fR, \fBmagic\fR, \fBformatter\fR, \fBlinter\fR, \fBcomment\fR,
+or \fBtabgives\fR
 command to an already defined syntax -- useful when you want to
 slightly improve a syntax defined in one of the system-installed
 files (which normally are not writable).