Update MVP.md, Web.md, and NonWeb.md.

Update HighLevelGoals.md to reflect Wasm's current goals

Update README.md, Nondeterminism.md, and Security.md

Replace the description of Wasm's Web API with a link to the spec

Update links.

Update references to IEEE 754-2008.

Modernize Contributing.md

Fix broken links Portability.md.

Replace FutureFeatures.md content with current links

Delete outdated pre-standard langauge description text.