6.1.0

Some small quality-of-life updates:

1. 83c4d37 merge className rather than overwriting it (needed for adding classes to fenced code blocks)
2. 46e474e multiple inline returns should be wrapped in a paragraph tag, not a div
3. 09a2885 export the markdown component as a functional component
4. 99c5e38 emit source maps for debugging

#3 ended up yielding some size benefits - the library is now ~4.75kB