New python module gdb.printing, and new commands info pretty-printer,

	New python module gdb.printing, and new commands info pretty-printer,
	enable pretty-printer, disable pretty-printer.
	* NEWS: Mention them.
	* data-directory/Makefile.in (PYTHON_FILES): Add gdb/printing.py,
	gdb/command/__init__.py, gdb/command/pretty_printers.py.
	* python/lib/gdb/__init__.py: Install pretty-printer commands.
	* python/lib/gdb/printing.py: New file.
	* python/lib/gdb/command/__init__.py: New file.
	* python/lib/gdb/command/pretty_printers.py: New file.

	doc/
	* gdb.texinfo (Pretty Printing): Expand into three sections,
	introduction, example, and commands.
	(Python API): Delete section Disabling Pretty-Printers, merge into
	Selecting Pretty-Printers.
	(Writing a Pretty-Printer): New section.  Move the pretty-printer
	example here, and reformat to match python coding style.  Add a second
	example using the gdb.printing module.
	(Python modules): Add gdb.printing.

	testsuite/
	* gdb.python/py-pp-maint.c: New file.
	* gdb.python/py-pp-maint.exp: New file.
	* gdb.python/py-pp-maint.py: New file.