configure script for hiredis

Here's simple configure.ac and Makefile.am for hiredis.

`hiredis-example-libev` and `hiredis-example-libevent` are automatically built when their pkg-config configuration are found.

    $ ./autogen.sh
    $ ./configure && make

I already merged [horms](https://github.com/redis/hiredis/pull/136)' request, commit 82fcf8e.

Thanks.