build: Separate building programs linking against libav* from building av*

This will allow cleaner integration of building example programs.
build: Integrate multilibrary examples into the build system

This includes moving libavformat/output-example to doc/examples/output.
aacsbr: Add some const casts to silence warnings in ff_sbr_apply()
Merge commit '14abeaa43d021afdce9119d906891abe89c03b88'

* commit '14abeaa43d021afdce9119d906891abe89c03b88':
  build: Separate building programs linking against libav* from building av*

Conflicts:
	Makefile
	doc/Makefile

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'ab81f24ad43bddf77ddd25cba86780c1c884996c'

* commit 'ab81f24ad43bddf77ddd25cba86780c1c884996c':
  build: Integrate multilibrary examples into the build system

Conflicts:
	configure
	doc/Makefile
	doc/examples/muxing.c
	doc/examples/output.c
	libavformat/Makefile
	libavformat/output-example.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Makefile: Fix building progs out of progs_g

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/Makefile fix PROGS

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  aacsbr: Add some const casts to silence warnings in ff_sbr_apply()

Conflicts:
	libavcodec/aacsbr.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>
configure: define CONFIG_THIS_YEAR at the configure level

The macro value can be shared between configure script and cmdutils.c.
cmdutils: remove this_year constant, use CONFIG_THIS_YEAR instead

Simplify.