Removed some obsolete code from a test. I'd copied and pasted. Tsk tsk.
Simplified some examples.
We can handle a gist with multiple files, as long as we specify everything and match the first file.
We can handle downloading any of the files of a gist with many files, as long as we specify everything.
We gracefully handle not matching any of the files of a gist with many files, as long as we specify everything.
We default to the first file of a gist with many files when we don't specify a filename; that's OK.
Removed whitespace.
We gracefully handle not finding the gist, both by wrong gist ID and by wrong username.
Moved optional parameter into the signature
We gracefully handle a failure downloading the gist.