v5.0.0

With version 5, Jet gets Go-like discard syntax (_ := stillRuns(), #168) and allows you to specify the argument slot of the piped value when pipelining (2 | repeat("foo", _), #169).

This means that _ is now a reserved symbol, as noted in v5's breaking changes: https://github.com/CloudyKit/jet/blob/master/docs/changes.md#v5.