tools: Add element-maker

tools: Add element-maker

Add a script that creates elements based on any of the GStreamer
base classes.  It isn't very user friendly at the moment, one
needs to edit the script to make it work properly.  Each base class
has a template file describing what to put into the constructed
element.  Eventually, these templates should be moved to reside
with the base class source and installed to a well-known directory,
where an installed script could find them.

The template files use the .c ending so editors know they are C
source, but gst-indent doesn't handle them correctly.  So they
need to be committed with -n.  Ugh.  I'll try to figure out a fix
for that soon.