doc: move fhs and mkShell under builders/special

In my opinion Functions should only contain pure functions. These are
both meant to provide derivations so I put them under Builders. Don't
know exactly *where* to put them so "special" it is...

doc/builders/special.xml

@@ -0,0 +1,12 @@
+<chapter xmlns="http://docbook.org/ns/docbook"
+         xmlns:xi="http://www.w3.org/2001/XInclude"
+         xml:id="chap-special">
+ <title>Special builders</title>
+ <para>
+  This chapter describes several special builders.
+ </para>
+ <xi:include href="special/fhs-environments.xml" />
+ <xi:include href="special/mkshell.xml" />
+</chapter>
+
+

doc/functions.xml

@@ -9,8 +9,6 @@
  <xi:include href="functions/library.xml" />
  <xi:include href="functions/generators.xml" />
  <xi:include href="functions/debug.xml" />
- <xi:include href="functions/fhs-environments.xml" />
- <xi:include href="functions/shell.xml" />
  <xi:include href="functions/prefer-remote-fetch.xml" />
  <xi:include href="functions/nix-gitignore.xml" />
 </chapter>

doc/manual.xml

@@ -25,6 +25,7 @@
   <title>Builders</title>
   <xi:include href="builders/fetchers.xml" />
   <xi:include href="builders/trivial-builders.xml" />
+  <xi:include href="builders/special.xml" />
   <xi:include href="builders/images.xml" />
   <xi:include href="languages-frameworks/index.xml" />
   <xi:include href="packages/index.xml" />