Added the body of the request to the context

[SamVerschueren]

Fixed https://github.com/dartist/express/issues/6 by adding a body property to the context.

var app = new Express()
  ..post('/mail', (ctx) {
    var name = ctx.body['name'];
    var mail = ctx.body['mail'];
  });

[mythz]

great stuff, thx.