Add a change-log to this repo

[ashmaroli]

Add a CHANGELOG.md to document relevant changes.

• Incorporate info from Releases for changes in released versions.
• Add current unreleased changes.

Format Guide:

• Version Heading: ### [VERSION] / [Release-Date: YY-MM-DD]
• Section Heading: #### [Title]
• Links to PRs:
  • Reference-links in bold with inline-code-formatting further enclosed in square-brackets.
  • Single-link: **[['#PR-No.'][]]**
  • Mutiple-links: **[['#PR-No.1'][], ['#PR-No.2'][]]**
  • Hyperlink: within the same section.

Example:

### 0.1.0 / 2017-01-01

#### Minor Improvements

  * Added Changelog. **[[`#1`][]]**
  * Added a cool feature. **[[`#2`][], [`#3`][]]**

[`#01`]: https://github.com/ashmaroli/jekyll-data/pull/1
[`#02`]: https://github.com/ashmaroli/jekyll-data/pull/2
[`#03`]: https://github.com/ashmaroli/jekyll-data/pull/3

#### Bug Fixes