Vision should make a positive statement of how the Web should evolve

The W3C’s Vision for the World Wide Web section contains 4 points that mostly describe ways to "not mess up", with no pointers toward what we should be trying to do.

We should work toward having a W3C-wide positive vision for the web, but I think it's ok to publish this version (consensus on "don't break things" is a step forward), and then develop that direction for the next version.