cmake

Hi Vinzenz,

I'm guessing you're perfectly happy with the current build system based on the conversation in your pyston pull request, but if you're interested, this is what cmake would like for libpypa. Feel free to discard this pull request.

Advantages

* Pyston Integration
 * Much better integration with pyston (moving to cmake) and double-conversion. Combining projects that both use cmake is a one liner. Problems like lib location go away.

* IDE support
 * You don't need to commit your IDE project files because cmake can generate them for your favorite IDE. Users can choose whichever IDE they prefer with zero setup required. With qt creator you can directly open CMakeLists.txt file and build, debug, etc within the IDE.

* Build times
 * Total autogen.sh, configure, and parallel build time is about 45 seconds on my machine. Cmake configure and build is only 8 seconds.

* Windows support
 * With a few minor changes (compiler flags mostly) you could generate a visual studio project and build libpypa on windows today. My experience with autotools on Windows was a nightmare.

* Packaging
 * It's very easy with CPack to create an rpm, dpkg, tarball, or even windows installer for the project.