Improve robustness of online check.
Cleanly close connection after checking remote URL.
Remove deprecated API call.
Move remote image not existing tests into Direct.
Remove clean target (already covered by git clean).
Factor out command.
Handle help manually.
Add tests for --help and an invalid option.
Simplify specification of defaults.
Factor out default header strings and separate metadata tests.
Factor out JPG, PNG filenames and sizes.
Factor out CID tests.
Fix broken import.
Cleanup basic tests.
Refactor FaultyAttachments to work as AttachmentDetection.
Enhance time-frozen tests - closes #38
Cleanup test titles.
Bump version.