Add missing file from previous commit.

TBR=@arv

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1454

Closes #1454.
Make types work in placeholder parser

This requires the parser to take an option object.
PlaceholderParser: Allow null in type context

This is so that you can do:

  parseStatement `var x: ${null};`

result in

  var x;
Add support for class member variable
Type asserts: Fix issues with TypeName and asserts

The assert functions we used for testing was wrong. It did not
handle number vs Number.

We also dropped the `moduleName` of the TypeName on the floor.
Add test case to verify compile to register format with name

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1470

Closes #1470.
Update README.md

Fixed link to wiki Getting Started page
Support sourcemaps in node execution.

Add dev-dependency on source-map-support.
Add --sourcemaps=memory option to store sourcemap in memory (actually
to not store it as data URL or file on disk.
When sourcemap option selected, supply sourcemap out of memory cache.
Replace Loader.getSourceMapInfo() based on codeUnit lookup with
Loader.getSourceMap(outputName).