Auditree-framework

- [FIXED] Reading raw evidence in checks is now supported.
- [FIXED] Cleaned up Design Principles document formatting.
- [FIXED] Virtual environment creation syntax corrected in Quick Start document.
- [ADDED] Binary content fetcher and checks included in demo examples.

- [CHANGED] GitHub Issues notifier can create issues for a subset of an accreditation's checks with a new configuration element.

- [FIXED] Github service `Github.get_issue_comments` returns all issue comments now.

- [ADDED] Storing raw evidence as binary content is now possible.

- [CHANGED] Improved selective fetcher bulk execution performance.

- [ADDED] Selective fetcher bulk `--include` and `--exclude` execution is now possible.