Feature/issue 109 gp updates

[rtrangucci]

Submission Checklist

• [x] Ran scripts to make sure all run correctly.

Summary:

Updates GP example models to latest code examples in the manual. Addresses #109

Intended Effect:

Increase efficiency of GP example models, introduce new GP models

How to Verify:

Run gp_fit.R, which should fit the marginal likelihood GP and the latent-variable GP with Gaussian observations.

Side Effects:

None

Documentation:

None

Reviewer Suggestions:

@betanalpha

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):

Rob Trangucci

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[bob-carpenter]

You can just go ahead and do your own merges here on the example-modesl repo.