documentation: Added the memory-resident BitBake feature

The main changes are captured in a new section devoted to the
oe-init-build-env-memres script within the ref-structure.xml
file and in the variables.xml file in a BBSERVER variable entry
in the glossary.

All other changes were necessary to integrate the new functionality
into areas where running the setup script are discussed.  Before
this feature, there was a single setup script (oe-init-build-env).
Consequently, wordings and such were designed exclusively for this
single method.  With the introduction of a second possible method
to initialize the build environment, tweaks to many sections were
needed.  Beside the wording tweaks, appropriate cross-referencing
was also needed.

All these changes cover the integration of the new feature.

Reported-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(From yocto-docs rev: c55c9a53c9b4cd1e06e6e81e32d56f9bbf5fe98c)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/faq.xml

@@ -682,9 +682,11 @@
             <para>
                 Yes - you can easily do this.
                 When you use BitBake to build an image, all the build output
-                goes into the directory created when you source the
+                goes into the directory created when you run the 
+                build environment setup script (i.e.
                 <link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>
-                setup script.
+                or
+                <link linkend='structure-memres-core-script'><filename>oe-init-build-env-memres</filename></link>).
                 By default, this <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
                 is named <filename>build</filename> but can be named
                 anything you want.