Fix compilation on Mac OSX 10.9.1

I've managed to get hadoofus compiling on OSX 10.9.1 which a bunch of code and makefile changes, and I've also added the ability to specify the `CC=".."` variable to switch out the `gcc` compiler for something else.

- Already have Cython installed
- Compiled using `/usr/bin/gcc`

```
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.0.2
Thread model: posix
```

These contributions by Tom Arnfeld @ Duedil Ltd are under the MIT license.

*Note: This pull request is a cleaned up version of #10*