Add ability to pass in a custom parser (for server-side-rendering).

[te-online]

Potentially fixes #6.

See discussion in #18.

This approach adds a parser property, which enables you to use the parser of your choice, when server-side-rendering.

parser – With this property you can pass in a custom parser, such as dom-parser. This enables you to do server-side-rendering.

Example

const parser = typeof document==='undefined' && require('dom-parser');
render(<Markup parser={parser} markup="<em>hello!</em><h1>asdflkj</h1>" />);

What do you think?

[danielweck]

Follow up: #6 (comment)