WIP API endpoint for tags
Work on agents in tags api
Renamed api.tag to api.tags

A plural form is more consistent with the other modules in the same
package.
Post endpoint for agents-in-tag api
Removed debug log statements
Rename AgentsInTagAPI to AgentsInTagIndexAPI
Docstring updates
Use plural for tag in api endpoint for consistency
Include hrefs pointing to referenced agents

Apparently, this is more in line with the general idea behind RESTful
web services.