loo v0.1.4

This update makes it easier for other package authors using loo to write
tests that involve running the loo function. It also includes minor bug
fixes and additional unit tests. Highlights:

• Don't call functions from parallel package if cores=1.
• Return entire vector/matrix of smoothed weights rather than a summary statistic when psislw function is called in an interactive session.
• Test coverage > 80%

loo-reference-0.1.4.pdf