Update links for docs

[ahartikainen]

Summary:

Current emcee link doesn't work. Also update to pymc3.

Intended Effect:

How to Verify:

Side Effects:

Documentation:

Reviewer Suggestions:

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Ari Hartikainen By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: GPLv3 (http://opensource.org/licenses/GPL-3.0)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[ahartikainen]

Merging without review. The current link is not safe.