improved regex, fixed bug, made tests

Hi

As promised, this pull request provides the tests (via doctest) for ignoring specified tags (functionality provided in the process_ignores function).

In addition, this pull request does the following:
 
 1. Vastly improves the regex for ignoring things: It is now more robust (it will ignore inline styles and ids provided in such tags - in fact, the ... will be ignored in the tag `<pre...>`, thereby matching things like `<pre id='test'>` etc
 2. Fixed bug (although this bug was more of an annoyance than anything else). It was possible that the list that was returned by the function would have as a last item an empty string '' to ignore. A simple check fixes this.
 3. Doctests are provided: Only three tests are given, but IMHO, it is enough.

The code also follows PEP 8, except for the doctstring which are longer than 79 characters.