Updated for Python 3.2.

Changed a single line of code to allow for execution under Python 3.2. Apparently, once the string returned from the `hmac.digest()` function, it doesn't need to be converted from Unicode character to an integer in Python 3.2. Therefore, we use a `try` block to catch this error, and react accordingly.

Also updated the documentation to reflect the new changes, and to highlight valid inputs for Python 3 compatibility. Also added a `.gitignore` file.