Add v1.0.0-beta spec.

Copied from https://raw.github.com/mojombo/semver.org/a16c419f09b5c5a26320317fcd331264daae16ef/index.md. Ref issue #52.
Label it as a beta.
Link to 1.0.0-beta.
Update to 2.0.0 RTM version of spec
Add latest spec changes
Fix link to the rc2 version.
Merge pull request #64 from mojombo/release-2.0

Release 2.0
Merge pull request #56 from theory/1.0.0-beta

1.0.0 beta
Make v2.0.0 link a permalink

Fixes #67
Reverting changing the spec link

Not sure why /spec/v2.0.0.html is 404ing.
Add front matter to SemVer 2.0.0 spec md file
Add link to 2.0.0

This really fixes #67