6 new translations, brand new identity, and more.

### Added
- New visual identity by @tylerfortune8.
- Version navigation.
- Links to latest released version in previous versions.
- "Why keep a changelog?" section.
- "Who needs a changelog?" section.
- "How do I make a changelog?" section.
- "Frequently Asked Questions" section.
- New "Guiding Principles" sub-section to "How do I make a changelog?".
- Simplified and Traditional Chinese translations from @tianshuo.
- German translation from @mpbzh.
- Italian translation from @roalz.
- Swedish translation from @magol.
- Turkish translation from @karalamalar.
- French translation from @zapashcanon.
- Brazilian Portugese translation from @aisamu.
- Polish translation from @amielucha.

### Changed
- Start using "changelog" over "change log" since it's the common usage.
- Start versioning based on the current English version at 0.3.0 to help
translation authors keep things up-to-date.
- Rewrite "What makes unicorns cry?" section.
- Rewrite "Ignoring Deprecations" sub-section to clarify the ideal
  scenario.
- Improve "Commit log diffs" sub-section to further argument against
  them.
- Merge "Why can’t people just use a git log diff?" with "Commit log
  diffs"
- Fix typos in Simplified Chinese and Traditional Chinese translations.
- Fix typos in Brazilian Portugese translation.
- Fix typos in Turkish translation.
- Fix typos in Czech translation.
- Fix typos in Swedish translation.
- Improve phrasing in French translation.
- Fix phrasing and spelling in German translation.

### Removed
- Section about "changelog" vs "CHANGELOG".

Russian, Brazilian Portugese, Spanish translations.

It's not just about open source

Should you ever rewrite a change log?

Fix factual error on date formats, typos, and erroneous links.

### Changed
- Update year to match in every README example.
- Reluctantly stop making fun of Brits only, since most of the world
  writes dates in a strange way.

### Fixed
- Fix typos in recent README changes.
- Update outdated unreleased diff link.

Acknowledge GNU change log style, point to ISO 8601, clean links.

README section on 'yanked' releases.

Markdown links to tags on versions headings.

Remove empty sub-section headers, use "change log" instead of "CHANGE…

…LOG" when not referring to the file itself.

Added "Why should I care?" section in README.