cmake: remove current,age,rev versioning calculations

The result is the same,
but we set VERSION and SOVERSION directly as version numbers
and not with the difficult to understand libtool interface numbers.
autotools: libtool version-info -> version-number

The calculation of current:revision:age for libtool version-info
is error-prone.
We now use MAJOR.MINOR.PATCH as defined in http://semver.org,
but we start with that already at 0.0.0, not with version 1.

The result is the same. Libtool takes the -version-number parameter
instead.

Additionally we only have two places were we define version numbers:
The main cmake and autotools files.
We have to define the version twice in configure.ac
due to AC_INIT limitations/warnings.

The corresponding ticket is
http://tickets.musicbrainz.org/browse/LIB-32
cmake: also clean files generated from .in

With cmake "make clean" should remove all derived files
except the cmakefils and the Makefile itself.
cmake: remove debug message
Revert "cmake: also clean files generated from .in"

Cmake still doesn't know how te recreate these automatically..
That feature might be in 2.8.11:
http://public.kitware.com/Bug/view.php?id=13582
but we don't want to depend on bleeding edge cmake anyways.

This reverts commit 63a5170bfea37373a4a94075c571505d34e8e32a.

Conflicts:
	CMakeLists.txt
LIB-24: support generic platform (cmake)

We now don't just fail when we don't know the platform.
We build for the "generic" platform.
No disc access is available, but discid_put works just fine.
LIB-24: support generic platform (autotools)

We issue a warning so packagers can check
if the platform is actually an alias for a supported platform.
In contrast to Cmake, in the autotools build
it is fairly difficult to actually see the warning.
Merge branch 'version_cleanup'

We stop using current, revsion, age with libtool -version-info.
We use -version-number now.

This only leads to changes on NetBSD (when using their autotools),
but libtool versioning is broken on BSD anyways.

See details in:
http://tickets.musicbrainz.org/browse/LIB-32
add .gitignore for cmakefiles
add autotools files to gitignore
autotools: add docs target
add notes about docs and BSD in INSTALL
create ChangeLog for 0.4.0
update AUTHORS
update Doxygen introduction
add get_version_string() for debug output
update ChangeLog for get_version_string()
cmake: fix versioninfo for out-of-source builds
set version to 0.4.0
actually document how get_feature_list() works