Remove redundant call to .replace() in url.js

Thanks to @errorx666 for the bug report, #869

Review URL: https://github.com/google/traceur-compiler/pull/871

Closes #871.
Add support for yield yield

Expand the yield expression if needed and transform that into a machine. Now we correctly support `yield (yield expr)`

Review URL: https://github.com/google/traceur-compiler/pull/866

Closes #866.
Add support for yield in if condition

If the condition of an if statement contains a yield we create a state machine for that expression.

Review URL: https://github.com/google/traceur-compiler/pull/867

Closes #867.
Add support for yield in switch expression

This allows us to support

```js
switch (yield expr) {
```

Review URL: https://github.com/google/traceur-compiler/pull/868

Closes #868.
Update README.md
CPS Transformer: Add support for yield expressions in while

Review URL: https://github.com/google/traceur-compiler/pull/872

Closes #872.
Synchronize highlighting of the transcoded tokens to the
cursor on the input tokens in repl.html.

Implement SourceMapRanger to aid in sourcemap uses.
Refactor repl-module to extrace repl-options module.