Allow HistogramLogReader to read file objects

[Mirochill]

Summary:

• Allow HistogramLogReader to accept either a path or a file-like object with readline().
• Decode byte lines as UTF-8 so binary handles, including zipfile.open(), can be read directly.
• Keep caller-owned file objects open when HistogramLogReader.close() is called, and add a regression test for that behavior.

Fixes #28.

Validation:

• Not run locally.

[ahothan]

Just curious what motivates you to submit so many PRs on so many git repositories @Mirochill ?