Add reference to additional Python tools and fix missing link

[felixocker]

Even though most of the tools listed at semantic-python-overview probably do not qualify for being included here, the link might still be helpful for someone who wants to dive deeper. Also, the link for Awesome Semantic Web was missing, so I added that too. I hope this is okay.

[dbooth-boston]

Excellent, thanks, I meant to include that link but forgot!