Only support queries which start with posts
Validate the host name to avoid bad requests

At first we validate for wsu.edu domains, but we'll add a filter
to make it easier to use for other things
Add a filter to validate domains that are not part of wsu.edu
We only support JSON format now, so don't pretend otherwise
Add support for a count argument to return a number of results
Merge pull request #2 from washingtonstateuniversity/validate

[PR] Validate attributes passed to the shortcode