Change API (see comments)

The API has been redesigned following directions given by Alexandre
Bertails (bertails@w3.org). This project is considered a prototype;
there may be subsequent changes to the design.
Add ParsedDocument implementation
Add Check implementation
Fix DocumentResource

Closes http client.
Add toString() to Assertion
Fixes header retrieval
Add unit tests for ParsedDocument and I18nChecker
Fix DocumentResource and ParsedDocument
Update ParsedDocument and ParsedDocumentTest
Add test resources (HTML files)
Add CheckTest
Add DocumentResourceTest
Add I18nTestRunner and related classes

These classes follow 'class.Test.php' and 'tests/index.php' from the old
project. They use the same remote resouces for testing, hosted at:
http://www.w3.org/International/tests/i18n-checker/generate .

Adds 'commons-configuration' as a dependency.
Add equals and hashCode to Assertion
Update Check
Update ParsedDocument
Update license in AssertionTest