Connector: Constant

[federico-razzoli]

This is a virtual Connector. It will accept queries that are actually sequences of one or more literal values. Every query execution will generate those constant values. It will also support a couple of constants starting with :, like :pi or :e. In the query, each value will be on a separate line. For example:

- query: |-
    42
    :pi

Why is this useful?

1. Draw a horizontal line that represents some threshold.
2. Show that a Connector is actually anything that generates values.