Fix ena_query()

[stitam]

Related to #101.

This PR:

• Adds a new argument include_links to ena_query().
• Updates the obsolete (I think) syntax which used a single url to the header, body, etc. syntax, which fixes the issue.
• Adds a convenience function project_url() which always returns the project URL for the package in which it was called.
• Adds project_url() to API requests to identify the package to the web API, avoiding anonymous requests.