First skeleton for user manual.

2013-07-05  Didier Verna  <didier@didierverna.net>

	* doc/user.texi: New file.
	* doc/Makefile (TEXI_FILES): Add it.
	* Makefile (INSTALL): New target.
	* INSTALL: Generate it from the user manual.
	* .gitignore: Update for user manual files.