Add basic .travis.yml

Add a simple .travis.yml file to test CyToolz on Python 2.6, 2.7, 3.2, and 3.3.  Addresses issue #7.

This uses the developmental version of `toolz` from github.  For releases of `cytoolz`, we may want to create a branch that tests against a specific version of `toolz` obtained via pip.

Cython is installed via pip.  No version is specified.  If it is ever needed, we could use a build matrix to test against several versions of Cython.  I don't know what the minimum required version of Cython is for CyToolz.

We do not yet distribute *.c files and neither do we test building them without Cython.