Adding-emitter example for User Guide [ci skip]

Add an example on adding an emitter to an existing builder,
based on a mailing-list discussion with Jeremy Elson.

Also:

* Try to model "best practice" by changing instances of hand-modifying
  env['ENV']['PATH'] in examples to using AppendENVPath function.
* Fixed a couple of Py2-style print statements.
* Tweaked markup on a couple of instances of site_scons.
* Black-formatted examples in the two userguide sections that
  were otherwise modified.
* Dropped old cons doc content which was included as a big
  comment at the fromt of builders-writing.xml.

Signed-off-by: Mats Wichmann <mats@linux.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/generated/examples/builders_adding_emitter_1.xml b/doc/generated/examples/builders_adding_emitter_1.xml
new file mode 100644
index 0000000..261b428
--- /dev/null
+++ b/doc/generated/examples/builders_adding_emitter_1.xml
@@ -0,0 +1,13 @@
+<screen xmlns="http://www.scons.org/dbxsd/v1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">% <userinput>scons -Q --tree=prune</userinput>
+cc -o hello.o -c hello.c
+cc -o hello -Wl,-Map=hello.map,--cref hello.o
++-.
+  +-SConstruct
+  +-hello
+  | +-hello.o
+  |   +-hello.c
+  +-hello.c
+  +-hello.map
+  | +-[hello.o]
+  +-[hello.o]
+</screen>