Renaming targets

[John Mandereau]

Hi,

This is a follow-up of thread "Why is it _still_ so freaking hard to get 
info with images?"
http://lists.gnu.org/archive/html/lilypond-devel/2009-03/msg00144.html

I had the changes for this for weeks in my working tree; it mainly 
renames targets to use more standard names:

web -> doc
web-1 -> doc-1
web-clean -> doc-clean
web-install -> install-doc
web-uninstall -> uninstall-doc
info-install -> install-info


I also added a hook to generate INSTALL.txt and README.txt when 
autogen.sh is successful from a Git checkout.

The patch including updates to "make help" and the documentation is 
reviewable at
http://codereview.appspot.com/49066/

Best,
John