Adds Markdown support

Added markdown support for snippets based on issue #7

Contribution Merger

Merged the pull request from @thierrymichel

Added support for extension dependancies

updated the package manifest to include dependency extensions when install Jekyll Snippets.

If you DO NOT have liquid language support extension installed VS Code will prompt you that the extension is needed for the Jekyll Snippets to work.

0.3.1: new snippets (#5)

this release is to bring Github and the vsce minor releases in sync