Base64, gitlab and gist

[alexisfrjp]

• Refactoring

• Add support for base64, gitlab and gist.

• Add a test.json to test in a browser with http://localhost:3000/***

• npm test passed with no error and no warning.

[drom]

LGTM. Thank you for your contribution.

[drom]

I have deployed it on AWS.

[drom]

We should add all these examples to https://github.com/wavedrom/server docs.