Unixify user interface

[flosell]

Currently, the CLI interface is organized around a very specific workflow and is convenient if you are using that specific workflow. Everything that's not that workflow is hard (e.g. generating a policy for a very specific selection of events, only fetching and printing certain events and then post-processing them with another tool (e.g. jq)).

For this reason, it would be nice if the trailscraper commands behaved more according to the Unix philosophy and only do one thing.

Proposal:

trailscraper generate-policy --from "one day ago" becomes trailscraper select --from "one day ago" | trailscraper generate

Concerns:

Performance impact of piping?

[flosell]

Done. Piping has a performance impact but is ok when traded off against the flexibility of the interface . Created #44 to work on inefficiencies.