Modernize configure.ac

- Update AC_INIT and AM_INIT_AUTOMAKE as per [1]
- Update AC_OUTPUT as per [2]

[1]: http://www.gnu.org/software/automake/manual/html_node/Public-Macros.html
[2]: http://www.gnu.org/software/autoconf/manual/html_node/Obsolete-Macros.html
Bump for 0.5