Corrected test function typo
Extended HTTP_METHODS with all(?) rfc'd HTTP methods
Refactored ExtensiblePattern.pathfor to avoid masking exceptions
Moved fresco.core.request_class to FrescoApp.request_class

This changes makes it possible to configure the request class used per
app rather than once globally. It also removes the need to import the
fresco.core module object itself.
Added _default arguments for route url generation
Renamed README so that it displays properly on github