Clean up debug output
Add code search

Code search results are content resources with an embedded repository.
The "content" and "encoding" attributes aren't returned and require
completion.
Add decoded_content property to ContentFile

The only encoding currently supported is base64, but that's ok, since
v3 of the GitHub API only mentions base64.
Fix add_attribute insertion logic

The code didn't work if it couldn't find a property in the file
that is lexicographically greater than the new attribute.
It now accepts _identity as an "end point" to insert before, and
empty lines in _initAttributes() and _useAttributes(), as they mark
the end of the method.

Also add "float" as a possible type, mainly for the "score" attribute
in search results.