various text improvements based on feedback
about : make sure that it does not sound like we want to replace other currencies
vocabulary : private keys are hosted remotely in the case of web servers
you-need-to-know : make clear that tor is used to hide IP, not log IP
how-it-works : various reformulations with few changes in the meaning
how-it-works : make clear that a confirmation is the result of an inclusion in the blockchain
use a lowercase "bitcoin" when speaking of the unit