What is the motivation for this pull request?

Feature: add option trim.

Resolves #155

What is the current behavior?

There is no way to remove whitespace text nodes.

What is the new behavior?

By passing option { trim: true }, whitespace text nodes are skipped:

parse('<br>\n', { trim: true }) // React.createElement('br')

This helps resolve the warning:

Warning: validateDOMNesting(...): Whitespace text nodes cannot appear as a child of <table>. Make sure you don't have any extra whitespace between tags on each line of your source code.

Checklist:

• Tests
• Documentation
• Types