Added section for Android configure cross-compile.

Android

=======

   See the build notes in the Android.mk file.

   Method using the static makefile:

      - see the build notes in the Android.mk file.

   Method using a configure cross-compile (tested with Android NDK r7b):

      - prepare the toolchain of the Android NDK for standalone use; this can

        be done by invoking the script:

        ./tools/make-standalone-toolchain.sh

        which creates a usual cross-compile toolchain. Lets assume that you put

        this toolchain below /opt then invoke configure with something like:

        export PATH=/opt/arm-linux-androideabi-4.4.3/bin:$PATH

        ./configure --host=arm-linux-androideabi [more configure options]

        make

      - if you want to compile directly from our GIT repo you might run into

        this issue with older automake stuff:

        checking host system type...

        Invalid configuration `arm-linux-androideabi':

        system `androideabi' not recognized

        configure: error: /bin/sh ./config.sub arm-linux-androideabi failed

        this issue can be fixed with using more recent versions of config.sub

        and config.guess which can be obtained here:

        http://git.savannah.gnu.org/gitweb/?p=config.git;a=tree

        you need to replace your system-own versions which usually can be

        found in your automake folder:

        find /usr -name config.sub

CROSS COMPILE