convert non-ASCII characters in json2 decoding

Non-ASCII characters in JSON strings are now decoded to UTF-8.
update known dialyzer warnings
Massive autotools refactoring & cleanup

Now, all makefile are generated from automake. This way, many things are more
configurable and maintainable.

Main (visible) changes:

 * Now, you can configure and compile Yaws outside the source directory. It is
   also possible to generate a archive for distribution, using the 'dist' rule
   (from now, 'distcheck' rule should always pass).

 * We track .erl dependencies using '-M*' flags of ERLC.

 * generated header 'yaws_configure.hrl' disappears. HAVE_SENDFILE,
   HAVE_ERLANG_SENDFILE and HAVE_CRYPTO_HASH macros are added in ERLC flags.

 * yaws_generated:localinstall/0 function disappears (see comment about local
   install).

 * To create a windows installer, we just need to run the 'mkinstaller'
   rule. Read win32/README.developer for details.

 * We use standard Erlang installation path for Yaws, relative to the erlang
   library directory (/usr/lib/erlang/lib). Now, '$(libdir)/yaws' is a link.

 * "local install" was removed. Now, to do a "developer install", we just need
   to set a prefix during the project configuration using --prefix option:
     $> ./configure --prefix=/path/to/yaws

 * DESTDIR variable is still supported.

Of course, many things can be changed during configuration and Rebar still works
as expected. Documentation needs to be updated and many tests should be done on
all supported platforms. It is a work in progress.