Added an explicit minimum version check.

Fixes #73
Removed .bat on pyreverse.
Using cygstart if available.
Added checks for missing editor and returncode.
Moved initial delay to launch.
Added Item IDs to each HTML header tag.
Added additional Markdown extensions.

This should mimic StackOverflow/GitHub.
Added clickable links.
Changed the error message for no default editor.
Moved the version check to __init__.py for wheels.
Merge pull request #75 from jacebrowning/version-check

Add an explicit minimum version check.
Added Item.parent_documents to mirror child.
Using real objects for export/publish tests.
Moved mock classes/data to the package.
Fixed duplicate iteration.
Skipping CSV/TSV in ref search.
Moved skipped extensions to a setting.
Added maxDiff.
Forced a sort order on child objects.
Documents can't be sorted.

I should really be testing this code before I push.