Added FastSpring to Services

Not a "VAT-handling service" per se in the way that Taxamo/VATAPI are, _but_ reading http://fastspring.com/faq under "International Customer Tax Collection & Management" says:

> Avoid the hassles of tax compliance by having FastSpring handle tax collection, compliance and payment on your behalf, including management of the European Union’s Value-Added Tax (VAT), US state sales taxes, and more.

so I'll probably be using them to sell my ebook through to avoid VAT headaches...