i2p project overview doc for the SDK

ok.  here's what I hope to be a final pass at the doc to be included
in the SDK when released Real Soon Now (aka under 72 hours).

It does still contain the controversial declaration of intent (we must
say why someone should bother writing an application with the SDK), but
its been tidied up a bit and caveated so as to help reduce any marginalizing
effects on those who don't have unqualified support for free, anonymous,
 and secure communication.  

Also the rest of the doc got some mods based on feedback.

So, read ASAP and post up your thoughts to the list so your concerns
can be addressed prior to packaging into the I2P SDK 0.1 release.  Anything
is fare game here - from issues with the content to spelling and grammar.

-jrandom