Parse attributes

Starting to get some better parsing action going on with this rewrite. 

```
unittest-suite-wait-for-done
PASS: ChromeIDLParser.docString.parse comment with **
PASS: ChromeIDLParser.docString.parse comment with ** multiline
PASS: ChromeIDLParser.docString.parse comment with *
PASS: ChromeIDLParser.docString.parse comment with * multiline
PASS: ChromeIDLParser.docString.parse comment with //
PASS: ChromeIDLParser.docString.parse comment with // multiline
PASS: ChromeIDLParser.attributeDeclaration.parse attribute with [instanceOf=Window]
PASS: ChromeIDLParser.attributeDeclaration.parse attribute with [nodoc]
PASS: ChromeIDLParser.attributeDeclaration.parse attribute with [legalValues=(16,32)]
PASS: ChromeIDLParser.attributeDeclaration.parse attribute with [nocompile, nodoc]

All 10 tests passed.
unittest-suite-success
```

Eventually wire this up into the main test runners