export DirectExportVisitor

Here's the pull request for #769.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/772

Closes #772.
Fix alphabetical ordering from last commit
Flexbox model for repl, reorg header UI, add link to github site

Flexbox model for repl, reorg header UI, add link to github site

This is based on #746

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/773

Closes #773.
Repl.html: Fix vertical alignment
Allow optional name for Loader.script(); default to empty string

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

Closes #774.
Experimental bundle support.
Add ModuleStore.register(name, deps, func), fills bundleStore[name].
Check bundleStore during load processing, after module registry,
before fetch.
If hit, create BundleCodeUnit, a TRANSFORMED codeUnit with
properties {deps, execute}.
The BundleCodeUnit participates in the remaining load processing.
See issue #754
Partial respond to partial review
Complete experiment. Fixes #754