Feature: Implement echo with no query

[miketheman]

When not passing anything to hq, it should echo back the HTML it received, potentially even with some formatting, a la jq, instead of current behavior which is to error.

$ curl -s https://example.com | hq
error: the following required arguments were not provided:
  <QUERY>

Usage: hq <QUERY> [INPUT_FILE]

For more information, try '--help'.

It'd be fine to also implement jq . as hq {} or such - as a way to verify that the HTML itself is parseable, prior to trying to apply a query.