Get rid of callouts since Markdown doesn't support them

doc/manual/src/expressions/arguments-variables.md

@@ -1,14 +1,21 @@
 # Arguments and Variables
 
+The Nix expression in [???](#ex-hello-nix) is a function; it is missing
+some arguments that have to be filled in somewhere. In the Nix Packages
+collection this is done in the file `pkgs/top-level/all-packages.nix`,
+where all Nix expressions for packages are imported and called with the
+appropriate arguments. Here are some fragments of `all-packages.nix`,
+with annotations of what they mean:
+
     ...
     
-    rec { 
+    rec { ①
     
-      hello = import ../applications/misc/hello/ex-1  { 
+      hello = import ../applications/misc/hello/ex-1 ② { ③
         inherit fetchurl stdenv perl;
       };
     
-      perl = import ../development/interpreters/perl { 
+      perl = import ../development/interpreters/perl { ④
         inherit fetchurl stdenv;
       };
     
@@ -20,20 +27,13 @@
     
     }
 
-The Nix expression in [???](#ex-hello-nix) is a function; it is missing
-some arguments that have to be filled in somewhere. In the Nix Packages
-collection this is done in the file `pkgs/top-level/all-packages.nix`,
-where all Nix expressions for packages are imported and called with the
-appropriate arguments. [example\_title](#ex-hello-composition) shows
-some fragments of `all-packages.nix`.
-
-  - This file defines a set of attributes, all of which are concrete
+1.  This file defines a set of attributes, all of which are concrete
     derivations (i.e., not functions). In fact, we define a *mutually
     recursive* set of attributes. That is, the attributes can refer to
     each other. This is precisely what we want since we want to “plug”
     the various packages into each other.
 
-  - Here we *import* the Nix expression for GNU Hello. The import
+2.  Here we *import* the Nix expression for GNU Hello. The import
     operation just loads and returns the specified Nix expression. In
     fact, we could just have put the contents of [???](#ex-hello-nix) in
     `all-packages.nix` at this point. That would be completely
@@ -44,7 +44,7 @@ some fragments of `all-packages.nix`.
     import a directory, Nix automatically appends `/default.nix` to the
     file name.
 
-  - This is where the actual composition takes place. Here we *call* the
+3.  This is where the actual composition takes place. Here we *call* the
     function imported from `../applications/misc/hello/ex-1` with a set
     containing the things that the function expects, namely `fetchurl`,
     `stdenv`, and `perl`. We use inherit again to use the attributes
@@ -68,5 +68,5 @@ some fragments of `all-packages.nix`.
     > 
     >     hello = callPackage ../applications/misc/hello/ex-1 { stdenv = myStdenv; };
 
-  - Likewise, we have to instantiate Perl, `fetchurl`, and the standard
+4.  Likewise, we have to instantiate Perl, `fetchurl`, and the standard
     environment.