Allow optional name for Loader.script(); default to empty string

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/774

Closes #774.
Repl.html: Don't hard code to use http

Also use link tag instead of @import to allow parallel downloads of resources.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/776

Closes #776.
Merge branch 'master' into gh-pages
Recompile