Fixing the analytics to capture the platform for SDK and Dartium downloads.

BUG=
R=shailentuli@google.com

Review URL: https://codereview.appspot.com/66610043
Add an explanation of which semver version pub uses.

Also update all semantic versioning links to point to version 2.0.0-rc.1.

BUG=14987
R=rnystrom@google.com, shaza@google.com

Review URL: https://chromiumcodereview.appspot.com//169873004
Fixed blockquote rendering
Merge pull request #303 from soimort/patch-1

Fixed a typo; fixed blockquote rendering
Upload link to code lab.

Review URL: https://chromiumcodereview.appspot.com/165793004